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5.x API

Note  注意

Express 5.0 requires Node.js 18 or higher.

express()

Creates an Express application. The express() function is a top-level function exported by the express module.
创建一个 Express 应用。 express() 函数是由 express 模块导出的顶级函数。

const express = require('express')
const app = express()

Methods  方法

express.json([options])  express.json([选项])

This is a built-in middleware function in Express. It parses incoming requests with JSON payloads and is based on body-parser.
这是 Express 中的一个内置中间件函数。它解析带有 JSON 负载的传入请求,基于 body-parser。

Returns middleware that only parses JSON and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.
返回一个仅解析 JSON 且仅查看请求头 Content-Type 与选项 type 匹配的中间件。该解析器接受任何 Unicode 编码的请求体,并支持自动解压 gzipdeflate 编码。

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.
中间件(即 req.body )执行后,一个新的 body 对象会被填充到 request 对象中,其中包含解析后的数据;若无请求体可解析、 Content-Type 未匹配或发生错误,则填充 undefined

As req.body’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.body.foo.toString() may fail in multiple ways, for example foo may not be there or may not be a string, and toString may not be a function and instead a string or other user-input.
由于 req.body 的结构基于用户控制的输入,该对象中的所有属性和值均不可信,应在信任前进行验证。例如, req.body.foo.toString() 可能以多种方式失败: foo 可能不存在或非字符串类型,而 toString 可能不是函数而是字符串或其他用户输入。

The following table describes the properties of the optional options object.
下表描述了可选对象 options 的属性。

Property  属性 Description  描述 Type  类型 Default  默认值
inflate Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected.
启用或禁用处理压缩(deflated)的请求体;禁用时,压缩的请求体会被拒绝。
Boolean  布尔值 true
limit Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing.
控制请求体的最大尺寸。若为数字,则该值指定字节数;若为字符串,则该值会被传递给字节库进行解析。
Mixed  混合类型 "100kb"
reviver The reviver option is passed directly to JSON.parse as the second argument. You can find more information on this argument in the MDN documentation about JSON.parse.
reviver 选项直接作为第二个参数传递给 JSON.parse 。关于此参数的更多信息,可查阅 MDN 文档中有关 JSON.parse 的部分。
Function  函数 null
strict Enables or disables only accepting arrays and objects; when disabled will accept anything JSON.parse accepts.
启用或禁用仅接受数组和对象;禁用时将接受 JSON.parse 所接受的任何内容。
Boolean  布尔值 true
type This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like json), a mime type (like application/json), or a mime type with a wildcard (like */* or */json). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value.
此选项用于确定中间件将解析的媒体类型。该选项可以是字符串、字符串数组或函数。若非函数, type 选项会直接传递给 type-is 库,可以是扩展名(如 json )、MIME 类型(如 application/json )或带通配符的 MIME 类型(如 */**/json )。若为函数,则调用 type 选项为 fn(req) ,若返回真值则解析请求。
Mixed  混合 "application/json"
verify This option, if supplied, is called as verify(req, res, buf, encoding), where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error.
如果提供此选项,它将被作为 verify(req, res, buf, encoding) 调用,其中 buf 是原始请求体的 Bufferencoding 是请求的编码。通过抛出错误可以中止解析过程。
Function  函数 undefined

express.raw([options])  express.raw([选项])

This is a built-in middleware function in Express. It parses incoming request payloads into a Buffer and is based on body-parser.
这是 Express 中的一个内置中间件函数。它将传入的请求负载解析为 Buffer ,并基于 body-parser。

Returns middleware that parses all bodies as a Buffer and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.
返回一个中间件,该中间件将所有请求体解析为 Buffer ,并且仅处理 Content-Type 请求头与 type 选项匹配的请求。此解析器接受任何 Unicode 编码的请求体,并支持自动解压 gzipdeflate 编码。

A new body Buffer containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.
中间件执行后(即 req.body ),会在 request 对象上填充一个包含解析数据的新 body Buffer ,如果没有可解析的请求体、 Content-Type 不匹配或发生错误,则填充 undefined

As req.body’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.body.toString() may fail in multiple ways, for example stacking multiple parsers req.body may be from a different parser. Testing that req.body is a Buffer before calling buffer methods is recommended.
由于 req.body 的结构基于用户控制的输入,此对象中的所有属性和值均不可信,应在信任前进行验证。例如, req.body.toString() 可能会以多种方式失败,比如堆叠多个解析器 req.body 可能来自不同的解析器。建议在调用 buffer 方法前验证 req.body 是否为 Buffer

The following table describes the properties of the optional options object.
下表描述了可选 options 对象的属性。

Property  属性 Description  描述 Type  类型 Default  默认
inflate Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected.
启用或禁用处理压缩(deflated)的请求体;禁用时,压缩的请求体会被拒绝。
Boolean  布尔值 true
limit Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing.
控制请求体的最大尺寸。如果值为数字,则指定字节数;如果为字符串,该值会传递给 bytes 库进行解析。
Mixed  混合 "100kb"
type This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like bin), a mime type (like application/octet-stream), or a mime type with a wildcard (like */* or application/*). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value.
此选项用于确定中间件将解析的媒体类型。该选项可以是字符串、字符串数组或函数。若非函数, type 选项会直接传递给 type-is 库,可以是扩展名(如 bin )、MIME 类型(如 application/octet-stream )或带通配符的 MIME 类型(如 */*application/* )。如果是函数, type 选项会作为 fn(req) 被调用,若返回真值则解析请求。
Mixed  混合 "application/octet-stream"
verify This option, if supplied, is called as verify(req, res, buf, encoding), where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error.
若提供此选项,它将被作为 verify(req, res, buf, encoding) 调用,其中 buf 是原始请求体的 Bufferencoding 是请求的编码。通过抛出错误可中止解析过程。
Function  函数 undefined

express.Router([options])
express.Router([选项])

Creates a new router object.
创建一个新的路由器对象。

const router = express.Router([options])

The optional options parameter specifies the behavior of the router.
可选的 options 参数指定了路由器的行为。

Property  属性 Description  描述 Default  默认值 Availability  可用性
caseSensitive Enable case sensitivity.
启用大小写敏感。
Disabled by default, treating “/Foo” and “/foo” as the same.
默认禁用,将“/Foo”和“/foo”视为相同。
 
mergeParams Preserve the req.params values from the parent router. If the parent and the child have conflicting param names, the child’s value take precedence.
保留父路由器的 req.params 值。如果父级和子级有冲突的参数名,以子级值为准。
false 4.5.0+
strict Enable strict routing.  启用严格路由。 Disabled by default, “/foo” and “/foo/” are treated the same by the router.
默认情况下禁用,路由器会将“/foo”和“/foo/”视为相同路径。
 

You can add middleware and HTTP method routes (such as get, put, post, and so on) to router just like an application.
你可以像应用程序一样,向 router 添加中间件和 HTTP 方法路由(例如 getputpost 等)。

For more information, see Router.
更多信息,请参阅路由器文档。

express.static(root, [options])

This is a built-in middleware function in Express. It serves static files and is based on serve-static.
这是 Express 中的一个内置中间件函数。它用于提供静态文件服务,基于 serve-static。

NOTE: For best results, use a reverse proxy cache to improve performance of serving static assets.
注意:为了达到最佳效果,建议使用反向代理缓存来提升静态资源服务的性能。

The root argument specifies the root directory from which to serve static assets. The function determines the file to serve by combining req.url with the provided root directory. When a file is not found, instead of sending a 404 response, it instead calls next() to move on to the next middleware, allowing for stacking and fall-backs.
参数 root 指定了提供静态资源的根目录。该函数通过将 req.url 与提供的 root 目录结合来确定要服务的文件。当文件未找到时,它不会发送 404 响应,而是调用 next() 以继续执行下一个中间件,从而实现堆叠和回退机制。

The following table describes the properties of the options object. See also the example below.
下表描述了 options 对象的属性。另请参阅下方的示例。

Property  属性 Description  描述 Type  类型 Default  默认值
dotfiles Determines how dotfiles (files or directories that begin with a dot “.”) are treated.
决定如何处理以点“.”开头的文件或目录(即点文件)。


See dotfiles below.  参见下方的点文件。
String  字符串 “ignore”  “忽略”
etag Enable or disable etag generation
启用或禁用 etag 生成


NOTE: express.static always sends weak ETags.
注意: express.static 总是发送弱 ETag。
Boolean  布尔值 true
extensions Sets file extension fallbacks: If a file is not found, search for files with the specified extensions and serve the first one found. Example: ['html', 'htm'].
设置文件扩展名回退:如果未找到文件,则搜索具有指定扩展名的文件并返回找到的第一个。示例: ['html', 'htm']
Mixed  混合类型 false
fallthrough Let client errors fall-through as unhandled requests, otherwise forward a client error.
让客户端错误穿透作为未处理的请求,否则转发客户端错误。


See fallthrough below.  参见下方的穿透设置。
Boolean  布尔值 true
immutable Enable or disable the immutable directive in the Cache-Control response header. If enabled, the maxAge option should also be specified to enable caching. The immutable directive will prevent supported clients from making conditional requests during the life of the maxAge option to check if the file has changed.
启用或禁用响应头中的 immutable 指令。若启用,还应指定 maxAge 选项以启用缓存。 immutable 指令将阻止支持的客户端在 maxAge 选项的生命周期内发起条件请求来检查文件是否已更改。
Boolean  布尔值 false
index Sends the specified directory index file. Set to false to disable directory indexing.
发送指定的目录索引文件。设置为 false 以禁用目录索引。
Mixed  混合 “index.html”
lastModified Set the Last-Modified header to the last modified date of the file on the OS.
Last-Modified 头设置为操作系统上文件的最后修改日期。
Boolean  布尔值 true
maxAge Set the max-age property of the Cache-Control header in milliseconds or a string in ms format.
设置 Cache-Control 头部 max-age 属性的值,单位为毫秒或 ms 格式的字符串。
Number  数值 0
redirect Redirect to trailing “/” when the pathname is a directory.
当路径名指向目录时,重定向至末尾带“/”的路径。
Boolean  布尔值 true
setHeaders Function for setting HTTP headers to serve with the file.
用于设置 HTTP 头部以配合文件服务的函数。


See setHeaders below.  参见下方的 setHeaders。
Function  函数  

For more information, see Serving static files in Express. and Using middleware - Built-in middleware.
更多信息,请参阅 Express 中的静态文件服务和使用中间件 - 内置中间件。

dotfiles  点文件

Possible values for this option are:
此选项的可能值为:

  • “allow” - No special treatment for dotfiles.
    “allow” - 对点文件不做特殊处理。
  • “deny” - Deny a request for a dotfile, respond with 403, then call next().
    “deny” - 拒绝点文件请求,响应为 403 ,然后调用 next()
  • “ignore” - Act as if the dotfile does not exist, respond with 404, then call next().
    “ignore” - 假装点文件不存在,响应为 404 ,然后调用 next()
fallthrough

When this option is true, client errors such as a bad request or a request to a non-existent file will cause this middleware to simply call next() to invoke the next middleware in the stack. When false, these errors (even 404s), will invoke next(err).
当此选项为 true 时,客户端错误如错误请求或请求不存在的文件将导致此中间件仅调用 next() 以触发堆栈中的下一个中间件。若为 false,这些错误(包括 404)将触发 next(err)

Set this option to true so you can map multiple physical directories to the same web address or for routes to fill in non-existent files.
将此选项设置为 true ,以便您可以将多个物理目录映射到相同的网络地址,或让路由填充不存在的文件。

Use false if you have mounted this middleware at a path designed to be strictly a single file system directory, which allows for short-circuiting 404s for less overhead. This middleware will also reply to all methods.
如果您已将此中间件挂载在严格设计为单一文件系统目录的路径上,请使用 false ,这样可以短路 404 错误以减少开销。此中间件还将响应所有方法。

setHeaders  设置头部

For this option, specify a function to set custom response headers. Alterations to the headers must occur synchronously.
对于此选项,指定一个函数来设置自定义响应头部。对头部的修改必须同步进行。

The signature of the function is:
函数的签名为:

fn(res, path, stat)

Arguments:  参数:

  • res, the response object.
    res ,响应对象。
  • path, the file path that is being sent.
    path ,正在发送的文件路径。
  • stat, the stat object of the file that is being sent.
    stat ,正在发送的文件的 stat 对象。

Example of express.static
express.static 的示例

Here is an example of using the express.static middleware function with an elaborate options object:
这里是一个使用 express.static 中间件函数配合详细选项对象的示例:

const options = {
  dotfiles: 'ignore',
  etag: false,
  extensions: ['htm', 'html'],
  index: false,
  maxAge: '1d',
  redirect: false,
  setHeaders (res, path, stat) {
    res.set('x-timestamp', Date.now())
  }
}

app.use(express.static('public', options))

express.text([options])  express.text([选项])

This is a built-in middleware function in Express. It parses incoming request payloads into a string and is based on body-parser.
这是 Express 中的一个内置中间件函数。它将传入的请求负载解析为字符串,并基于 body-parser。

Returns middleware that parses all bodies as a string and only looks at requests where the Content-Type header matches the type option. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.
返回一个中间件,该中间件将所有请求体解析为字符串,并且仅处理 Content-Type 头部与 type 选项匹配的请求。此解析器接受任何 Unicode 编码的请求体,并支持自动解压 gzipdeflate 编码。

A new body string containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred.
中间件处理后(即 req.body ),会在 request 对象上填充一个包含解析数据的新 body 字符串;如果没有可解析的请求体、 Content-Type 不匹配或发生错误,则为 undefined

As req.body’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.body.trim() may fail in multiple ways, for example stacking multiple parsers req.body may be from a different parser. Testing that req.body is a string before calling string methods is recommended.
由于 req.body 的结构基于用户控制的输入,该对象中的所有属性和值均不可信,应在信任前进行验证。例如, req.body.trim() 可能会以多种方式失败,比如堆叠多个解析器 req.body 可能来自不同的解析器。建议在调用字符串方法前测试 req.body 是否为字符串。

The following table describes the properties of the optional options object.
下表描述了可选 options 对象的属性。

Property  属性 Description  描述 Type  类型 Default  默认
defaultCharset Specify the default character set for the text content if the charset is not specified in the Content-Type header of the request.
如果请求的 Content-Type 头部未指定字符集,则为此文本内容指定默认字符集。
String  字符串 "utf-8"
inflate Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected.
启用或禁用处理压缩(deflated)的请求体;禁用时,压缩的请求体会被拒绝。
Boolean  布尔值 true
limit Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing.
控制请求体的最大尺寸。若为数字,则该值指定字节数;若为字符串,该值会被传递给字节库进行解析。
Mixed  混合类型 "100kb"
type This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like txt), a mime type (like text/plain), or a mime type with a wildcard (like */* or text/*). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value.
此选项用于确定中间件将解析的媒体类型。可以是字符串、字符串数组或函数。若非函数, type 选项会直接传递给 type-is 库,可以是扩展名(如 txt )、MIME 类型(如 text/plain )或带通配符的 MIME 类型(如 */*text/* )。若为函数, type 选项会作为 fn(req) 被调用,若返回真值则请求会被解析。
Mixed  混合 "text/plain"
verify This option, if supplied, is called as verify(req, res, buf, encoding), where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error.
如果提供此选项,它将被调用为 verify(req, res, buf, encoding) ,其中 buf 是原始请求体的 Buffer ,而 encoding 是请求的编码。通过抛出错误可以中止解析过程。
Function  函数 undefined

express.urlencoded([options])
express.urlencoded([选项])

This is a built-in middleware function in Express. It parses incoming requests with urlencoded payloads and is based on body-parser.
这是 Express 中的一个内置中间件函数。它解析带有 urlencoded 负载的传入请求,并基于 body-parser。

Returns middleware that only parses urlencoded bodies and only looks at requests where the Content-Type header matches the type option. This parser accepts only UTF-8 encoding of the body and supports automatic inflation of gzip and deflate encodings.
返回一个仅解析 urlencoded 请求体且仅查看请求头 Content-Type 与选项 type 匹配的中间件。此解析器仅接受 UTF-8 编码的请求体,并支持自动解压 gzipdeflate 编码。

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body), or undefined if there was no body to parse, the Content-Type was not matched, or an error occurred. This object will contain key-value pairs, where the value can be a string or array (when extended is false), or any type (when extended is true).
中间件执行后(即 req.body ),一个新的 body 对象包含解析后的数据会被填充到 request 对象上,若无请求体可解析、 Content-Type 未匹配或发生错误,则为 undefined 。此对象将包含键值对,其中值可以是字符串或数组(当 extendedfalse 时),或任意类型(当 extendedtrue 时)。

As req.body’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.body.foo.toString() may fail in multiple ways, for example foo may not be there or may not be a string, and toString may not be a function and instead a string or other user-input.
由于 req.body 的结构基于用户控制的输入,该对象中的所有属性和值均不可信,应在信任前进行验证。例如, req.body.foo.toString() 可能以多种方式失败,比如 foo 可能不存在或不是字符串,而 toString 可能不是函数而是字符串或其他用户输入。

The following table describes the properties of the optional options object.
下表描述了可选 options 对象的属性。

Property  属性 Description  描述 Type  类型 Default  默认
extended This option allows to choose between parsing the URL-encoded data with the querystring library (when false) or the qs library (when true). The “extended” syntax allows for rich objects and arrays to be encoded into the URL-encoded format, allowing for a JSON-like experience with URL-encoded. For more information, please see the qs library.
此选项允许选择使用 querystring 库(当 false 时)或 qs 库(当 true 时)来解析 URL 编码的数据。“扩展”语法允许将丰富的对象和数组编码为 URL 编码格式,从而在使用 URL 编码时获得类似 JSON 的体验。更多信息,请参阅 qs 库。
Boolean  布尔值 false
inflate Enables or disables handling deflated (compressed) bodies; when disabled, deflated bodies are rejected.
启用或禁用处理压缩(deflated)的请求体;禁用时,压缩的请求体会被拒绝。
Boolean  布尔值 true
limit Controls the maximum request body size. If this is a number, then the value specifies the number of bytes; if it is a string, the value is passed to the bytes library for parsing.
控制请求体的最大尺寸。若为数字,则该值指定字节数;若为字符串,该值会被传递给字节库进行解析。
Mixed  混合类型 "100kb"
parameterLimit This option controls the maximum number of parameters that are allowed in the URL-encoded data. If a request contains more parameters than this value, an error will be raised.
此选项控制 URL 编码数据中允许的最大参数数量。如果请求包含的参数超过此值,将引发错误。
Number  数字 1000
type This is used to determine what media type the middleware will parse. This option can be a string, array of strings, or a function. If not a function, type option is passed directly to the type-is library and this can be an extension name (like urlencoded), a mime type (like application/x-www-form-urlencoded), or a mime type with a wildcard (like */x-www-form-urlencoded). If a function, the type option is called as fn(req) and the request is parsed if it returns a truthy value.
此选项用于确定中间件将解析的媒体类型。该选项可以是字符串、字符串数组或函数。若非函数, type 选项会直接传递给 type-is 库,可以是扩展名(如 urlencoded )、mime 类型(如 application/x-www-form-urlencoded )或带通配符的 mime 类型(如 */x-www-form-urlencoded )。若为函数, type 选项会作为 fn(req) 调用,若返回真值则请求会被解析。
Mixed  混合 "application/x-www-form-urlencoded"
verify This option, if supplied, is called as verify(req, res, buf, encoding), where buf is a Buffer of the raw request body and encoding is the encoding of the request. The parsing can be aborted by throwing an error.
若提供此选项,它会被调用为 verify(req, res, buf, encoding) ,其中 buf 是原始请求体的 Bufferencoding 是请求的编码。解析过程可通过抛出错误来中止。
Function  函数 undefined

Application  应用

The app object conventionally denotes the Express application. Create it by calling the top-level express() function exported by the Express module:
通常, app 对象代表 Express 应用。通过调用 Express 模块导出的顶层 express() 函数来创建它:

const express = require('express')
const app = express()

app.get('/', (req, res) => {
  res.send('hello world')
})

app.listen(3000)

The app object has methods for
app 对象拥有以下方法用于

  • Routing HTTP requests; see for example, app.METHOD and app.param.
    路由 HTTP 请求;例如,参见 app.METHOD 和 app.param。
  • Configuring middleware; see app.route.
    配置中间件;参见 app.route。
  • Rendering HTML views; see app.render.
    渲染 HTML 视图;参见 app.render。
  • Registering a template engine; see app.engine.
    注册模板引擎;参见 app.engine。

It also has settings (properties) that affect how the application behaves; for more information, see Application settings.
它还包含影响应用程序行为的设置(属性);更多信息,请参阅应用程序设置。

The Express application object can be referred from the request object and the response object as req.app, and res.app, respectively.
Express 应用程序对象可以通过请求对象和响应对象分别引用为 req.appres.app

Properties  属性

app.locals

The app.locals object has properties that are local variables within the application, and will be available in templates rendered with res.render.
app.locals 对象拥有作为应用程序内局部变量的属性,这些属性将在使用 res.render 渲染的模板中可用。

The locals object is used by view engines to render a response. The object keys may be particularly sensitive and should not contain user-controlled input, as it may affect the operation of the view engine or provide a path to cross-site scripting. Consult the documentation for the used view engine for additional considerations.
视图引擎使用 locals 对象来渲染响应。该对象的键可能特别敏感,不应包含用户控制的输入,因为这可能影响视图引擎的运行或提供跨站脚本攻击的途径。有关更多注意事项,请查阅所用视图引擎的文档。

console.dir(app.locals.title)
// => 'My App'

console.dir(app.locals.email)
// => 'me@myapp.com'

Once set, the value of app.locals properties persist throughout the life of the application, in contrast with res.locals properties that are valid only for the lifetime of the request.
一旦设置, app.locals 属性的值将在应用程序的整个生命周期中持续存在,这与仅在请求生命周期内有效的 res.locals 属性形成对比。

You can access local variables in templates rendered within the application. This is useful for providing helper functions to templates, as well as application-level data. Local variables are available in middleware via req.app.locals (see req.app)
您可以在应用程序内渲染的模板中访问局部变量。这对于向模板提供辅助函数以及应用级数据非常有用。局部变量可通过 req.app.locals 在中间件中访问(参见 req.app)。

app.locals.title = 'My App'
app.locals.strftime = require('strftime')
app.locals.email = 'me@myapp.com'

app.mountpath

The app.mountpath property contains one or more path patterns on which a sub-app was mounted.
app.mountpath 属性包含一个或多个子应用挂载的路径模式。

A sub-app is an instance of express that may be used for handling the request to a route.
子应用是 express 的一个实例,可用于处理对某一路由的请求。

const express = require('express')

const app = express() // the main app
const admin = express() // the sub app

admin.get('/', (req, res) => {
  console.log(admin.mountpath) // /admin
  res.send('Admin Homepage')
})

app.use('/admin', admin) // mount the sub app

It is similar to the baseUrl property of the req object, except req.baseUrl returns the matched URL path, instead of the matched patterns.
这与 req 对象的 baseUrl 属性类似,不同之处在于 req.baseUrl 返回的是匹配的 URL 路径,而非匹配的模式。

If a sub-app is mounted on multiple path patterns, app.mountpath returns the list of patterns it is mounted on, as shown in the following example.
如果一个子应用挂载在多个路径模式上, app.mountpath 会返回其挂载的所有模式列表,如下例所示。

const admin = express()

admin.get('/', (req, res) => {
  console.log(admin.mountpath) // [ '/adm{*splat}n', '/manager' ]
  res.send('Admin Homepage')
})

const secret = express()
secret.get('/', (req, res) => {
  console.log(secret.mountpath) // /secr{*splat}t
  res.send('Admin Secret')
})

admin.use('/secr{*splat}t', secret) // load the 'secret' router on '/secr{*splat}t', on the 'admin' sub app
app.use(['/adm{*splat}n', '/manager'], admin) // load the 'admin' router on '/adm{*splat}n' and '/manager', on the parent app

app.router

The application’s in-built instance of router. This is created lazily, on first access.
应用程序内置的路由器实例。此实例在首次访问时延迟创建。

const express = require('express')
const app = express()
const router = app.router

router.get('/', (req, res) => {
  res.send('hello world')
})

app.listen(3000)

You can add middleware and HTTP method routes to the router just like an application.
您可以像对待应用程序一样,向 router 添加中间件和 HTTP 方法路由。

For more information, see Router.
更多信息,请参阅 Router。

Events  事件

app.on('mount', callback(parent))

The mount event is fired on a sub-app, when it is mounted on a parent app. The parent app is passed to the callback function.
当子应用挂载到父应用上时,会触发 mount 事件。父应用会被传递给回调函数。

NOTE  注意

Sub-apps will:  子应用将:

  • Not inherit the value of settings that have a default value. You must set the value in the sub-app.
    不会继承具有默认值的设置项的值。您必须在子应用中设置该值。
  • Inherit the value of settings with no default value.
    继承无默认值的设置项的值。

For details, see Application settings.
详情请参阅应用程序设置。

const admin = express()

admin.on('mount', (parent) => {
  console.log('Admin Mounted')
  console.log(parent) // refers to the parent app
})

admin.get('/', (req, res) => {
  res.send('Admin Homepage')
})

app.use('/admin', admin)

Methods  方法

app.all(path, callback [, callback ...])

This method is like the standard app.METHOD() methods, except it matches all HTTP verbs.
此方法与标准的 app.METHOD() 方法类似,但它匹配所有的 HTTP 动词。

Arguments  参数

Argument   参数 Description   描述 Default   默认值
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数数组。
  • A combination of all of the above.
    以上所有方式的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调能调用 next('route') 来跳过剩余的路由回调。此机制可用于对路由设置前置条件,若无继续当前路由的必要,则将控制权移交给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
有关示例,请参阅中间件回调函数示例。

None   

Examples  示例

The following callback is executed for requests to /secret whether using GET, POST, PUT, DELETE, or any other HTTP request method:
无论使用 GET、POST、PUT、DELETE 还是其他任何 HTTP 请求方法,以下回调都会针对 /secret 的请求执行:

app.all('/secret', (req, res, next) => {
  console.log('Accessing the secret section ...')
  next() // pass control to the next handler
})

The app.all() method is useful for mapping “global” logic for specific path prefixes or arbitrary matches. For example, if you put the following at the top of all other route definitions, it requires that all routes from that point on require authentication, and automatically load a user. Keep in mind that these callbacks do not have to act as end-points: loadUser can perform a task, then call next() to continue matching subsequent routes.
app.all() 方法对于为特定路径前缀或任意匹配映射“全局”逻辑非常有用。例如,如果你在所有其他路由定义的最前面放置以下代码,它将要求从该点开始的所有路由都需要认证,并自动加载用户。请记住,这些回调不必作为端点: loadUser 可以执行一个任务,然后调用 next() 以继续匹配后续路由。

app.all('{*splat}', requireAuthentication, loadUser)

Or the equivalent:  或等效于:

app.all('{*splat}', requireAuthentication)
app.all('{*splat}', loadUser)

Another example is white-listed “global” functionality. The example is similar to the ones above, but it only restricts paths that start with “/api”:
另一个例子是白名单中的“全局”功能。此示例与上述类似,但仅限制以“/api”开头的路径:

app.all('/api/{*splat}', requireAuthentication)

app.delete(path, callback [, callback ...])

Routes HTTP DELETE requests to the specified path with the specified callback functions. For more information, see the routing guide.
将 HTTP DELETE 请求路由到指定路径,并使用指定的回调函数。更多信息,请参阅路由指南。

Arguments  参数

Argument   参数 Description   描述 Default   默认值
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数数组。
  • A combination of all of the above.
    以上所有方式的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调可以调用 next('route') 来跳过剩余的路由回调。你可以利用这一机制为路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例请参见中间件回调函数示例。

None   

Example  示例

app.delete('/', (req, res) => {
  res.send('DELETE request to homepage')
})

app.disable(name)

Sets the Boolean setting name to false, where name is one of the properties from the app settings table. Calling app.set('foo', false) for a Boolean property is the same as calling app.disable('foo').
将布尔设置 name 设为 false ,其中 name 是应用设置表中的属性之一。对布尔属性调用 app.set('foo', false) 等同于调用 app.disable('foo')

For example:  例如:

app.disable('trust proxy')
app.get('trust proxy')
// => false

app.disabled(name)

Returns true if the Boolean setting name is disabled (false), where name is one of the properties from the app settings table.
如果布尔设置 name 被禁用( false ),则返回 true ,其中 name 是应用设置表中的属性之一。

app.disabled('trust proxy')
// => true

app.enable('trust proxy')
app.disabled('trust proxy')
// => false

app.enable(name)

Sets the Boolean setting name to true, where name is one of the properties from the app settings table. Calling app.set('foo', true) for a Boolean property is the same as calling app.enable('foo').
将布尔设置 name 设为 true ,其中 name 是应用设置表中的属性之一。对布尔属性调用 app.set('foo', true) 等同于调用 app.enable('foo')

app.enable('trust proxy')
app.get('trust proxy')
// => true

app.enabled(name)

Returns true if the setting name is enabled (true), where name is one of the properties from the app settings table.
如果设置 name 已启用( true ),则返回 true ,其中 name 是应用设置表中的属性之一。

app.enabled('trust proxy')
// => false

app.enable('trust proxy')
app.enabled('trust proxy')
// => true

app.engine(ext, callback)

Registers the given template engine callback as ext.
将给定的模板引擎 callback 注册为 ext

By default, Express will require() the engine based on the file extension. For example, if you try to render a “foo.pug” file, Express invokes the following internally, and caches the require() on subsequent calls to increase performance.
默认情况下,Express 会根据文件扩展名 require() 引擎。例如,若尝试渲染“foo.pug”文件,Express 内部会调用以下内容,并在后续调用中缓存 require() 以提高性能。

app.engine('pug', require('pug').__express)

Use this method for engines that do not provide .__express out of the box, or if you wish to “map” a different extension to the template engine.
对于不提供开箱即用 .__express 的引擎,或希望将不同扩展名“映射”到模板引擎时,可使用此方法。

For example, to map the EJS template engine to “.html” files:
例如,将 EJS 模板引擎映射到“.html”文件:

app.engine('html', require('ejs').renderFile)

In this case, EJS provides a .renderFile() method with the same signature that Express expects: (path, options, callback), though note that it aliases this method as ejs.__express internally so if you’re using “.ejs” extensions you don’t need to do anything.
在此情况下,EJS 提供了一个与 Express 预期签名相同的 .renderFile() 方法: (path, options, callback) ,但请注意,它在内部将此方法别名为 ejs.__express ,因此若使用“.ejs”扩展名则无需额外操作。

Some template engines do not follow this convention. The consolidate.js library maps Node template engines to follow this convention, so they work seamlessly with Express.
部分模板引擎并不遵循这一惯例。consolidate.js 库将 Node 模板引擎映射为遵循此惯例,以便它们能与 Express 无缝协作。

const engines = require('consolidate')
app.engine('haml', engines.haml)
app.engine('html', engines.hogan)

app.get(name)

Returns the value of name app setting, where name is one of the strings in the app settings table. For example:
返回@app 设置的值,其中 name 是应用设置表中的字符串之一。例如:

app.get('title')
// => undefined

app.set('title', 'My Site')
app.get('title')
// => "My Site"

app.get(path, callback [, callback ...])

Routes HTTP GET requests to the specified path with the specified callback functions.
将 HTTP GET 请求路由到指定路径,并执行相应的回调函数。

Arguments  参数

Argument   参数 Description   描述 Default   默认
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(用逗号分隔)。
  • An array of middleware functions.
    中间件函数数组。
  • A combination of all of the above.
    以上所有情况的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调可以调用 next('route') 来跳过剩余的路由回调。你可以利用这一机制为路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例可参见中间件回调函数示例。

None   

For more information, see the routing guide.
更多信息,请参阅路由指南。

Example  示例

app.get('/', (req, res) => {
  res.send('GET request to homepage')
})

app.listen(path, [callback])

Starts a UNIX socket and listens for connections on the given path. This method is identical to Node’s http.Server.listen().
启动一个 UNIX 套接字并在指定路径上监听连接。此方法与 Node 的 http.Server.listen()相同。

const express = require('express')
const app = express()
app.listen('/tmp/sock')

app.listen([port[, host[, backlog]]][, callback])
app.listen([端口[, 主机[, 积压数]]][, 回调函数])

Binds and listens for connections on the specified host and port. This method is identical to Node’s http.Server.listen().
在指定的主机和端口上绑定并监听连接。此方法与 Node 的 http.Server.listen()相同。

If port is omitted or is 0, the operating system will assign an arbitrary unused port, which is useful for cases like automated tasks (tests, etc.).
如果省略端口或设为 0,操作系统将分配任意一个未使用的端口,这对于自动化任务(如测试等)场景非常有用。

const express = require('express')
const app = express()
app.listen(3000)

The app returned by express() is in fact a JavaScript Function, designed to be passed to Node’s HTTP servers as a callback to handle requests. This makes it easy to provide both HTTP and HTTPS versions of your app with the same code base, as the app does not inherit from these (it is simply a callback):
express() 返回的 app 实际上是一个 JavaScript Function ,设计用于作为回调传递给 Node 的 HTTP 服务器以处理请求。这使得用相同的代码库提供 HTTP 和 HTTPS 版本的应用程序变得容易,因为应用程序并不继承这些(它只是一个回调):

const express = require('express')
const https = require('https')
const http = require('http')
const app = express()

http.createServer(app).listen(80)
https.createServer(options, app).listen(443)

The app.listen() method returns an http.Server object and (for HTTP) is a convenience method for the following:
app.listen() 方法返回一个 http.Server 对象,并且(对于 HTTP)是以下操作的便捷方法:

app.listen = function () {
  const server = http.createServer(this)
  return server.listen.apply(server, arguments)
}

Note  注意

All the forms of Node’s http.Server.listen() method are in fact actually supported.
实际上,Node 的 http.Server.listen()方法的所有形式都是被支持的。

app.METHOD(path, callback [, callback ...])
app.METHOD(路径, 回调函数 [, 回调函数 ...])

Routes an HTTP request, where METHOD is the HTTP method of the request, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are app.get(), app.post(), app.put(), and so on. See Routing methods below for the complete list.
路由一个 HTTP 请求,其中 METHOD 是该请求的 HTTP 方法,如 GET、PUT、POST 等,均为小写。因此,实际的方法包括 app.get()app.post()app.put() 等。完整列表请参见下方的路由方法。

Arguments  参数

Argument   参数 Description   描述 Default   默认
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
有关示例,请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数的数组。
  • A combination of all of the above.
    以上所有功能的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个回调函数,它们的行为类似于中间件,但这些回调可以通过调用 next('route') 来跳过剩余的路由回调。此机制可用于对路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例可参见中间件回调函数示例。

None   

Routing methods  路由方法

Express supports the following routing methods corresponding to the HTTP methods of the same names:
Express 支持以下路由方法,对应同名的 HTTP 方法:

  • checkout
  • copy
  • delete
  • get
  • head
  • lock
  • merge
  • mkactivity
  • mkcol
  • move
  • m-search
  • notify
  • options
  • patch
  • post
  • purge
  • put
  • report
  • search
  • subscribe
  • trace
  • unlock
  • unsubscribe

The API documentation has explicit entries only for the most popular HTTP methods app.get(), app.post(), app.put(), and app.delete(). However, the other methods listed above work in exactly the same way.
API 文档仅明确记录了最流行的 HTTP 方法 app.get()app.post()app.put()app.delete() 。然而,上面列出的其他方法以完全相同的方式工作。

To route methods that translate to invalid JavaScript variable names, use the bracket notation. For example, app['m-search']('/', function ....
要路由那些转换为无效 JavaScript 变量名的方法,请使用括号表示法。例如, app['m-search']('/', function ...

The app.get() function is automatically called for the HTTP HEAD method in addition to the GET method if app.head() was not called for the path before app.get().
如果在 app.get() 之前未对路径调用 app.head() ,则 app.get() 函数除了 GET 方法外,还会自动为 HTTP HEAD 方法调用。

The method, app.all(), is not derived from any HTTP method and loads middleware at the specified path for all HTTP request methods. For more information, see app.all.
方法 app.all() 并非源自任何 HTTP 方法,它会为所有 HTTP 请求方法在指定路径加载中间件。更多信息,请参阅 app.all。

For more information on routing, see the routing guide.
有关路由的更多信息,请参阅路由指南。

app.param(name, callback)
app.param(名称, 回调函数)

Add callback triggers to route parameters, where name is the name of the parameter or an array of them, and callback is the callback function. The parameters of the callback function are the request object, the response object, the next middleware, the value of the parameter and the name of the parameter, in that order.
向路由参数添加回调触发器,其中 name 是参数名称或其数组, callback 是回调函数。回调函数的参数依次为请求对象、响应对象、下一个中间件、参数值及参数名称。

If name is an array, the callback trigger is registered for each parameter declared in it, in the order in which they are declared. Furthermore, for each declared parameter except the last one, a call to next inside the callback will call the callback for the next declared parameter. For the last parameter, a call to next will call the next middleware in place for the route currently being processed, just like it would if name were just a string.
如果 name 是一个数组,那么 callback 触发器会按照声明的顺序为其中每个参数注册。此外,对于除最后一个参数外的每个声明参数,回调内部调用 next 将会触发下一个声明参数的回调。对于最后一个参数,调用 next 则会调用当前处理路由的下一个中间件,就像 name 仅是一个字符串时那样。

For example, when :user is present in a route path, you may map user loading logic to automatically provide req.user to the route, or perform validations on the parameter input.
例如,当路由路径中存在 :user 时,你可以将用户加载逻辑映射到该路由,自动提供 req.user ,或对参数输入执行验证。

app.param('user', (req, res, next, id) => {
  // try to get the user details from the User model and attach it to the request object
  User.find(id, (err, user) => {
    if (err) {
      next(err)
    } else if (user) {
      req.user = user
      next()
    } else {
      next(new Error('failed to load user'))
    }
  })
})

Param callback functions are local to the router on which they are defined. They are not inherited by mounted apps or routers, nor are they triggered for route parameters inherited from parent routers. Hence, param callbacks defined on app will be triggered only by route parameters defined on app routes.
参数回调函数的作用域仅限于定义它们的路由器。它们不会被挂载的应用或路由器继承,也不会因从父路由器继承的路由参数而触发。因此,在 app 上定义的参数回调仅由 app 路由上定义的路由参数触发。

All param callbacks will be called before any handler of any route in which the param occurs, and they will each be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples.
所有参数回调都会在包含该参数的任意路由的任何处理程序之前被调用,并且在一个请求-响应周期中,每个回调仅会被调用一次,即使该参数在多个路由中匹配也是如此,如下例所示。

app.param('id', (req, res, next, id) => {
  console.log('CALLED ONLY ONCE')
  next()
})

app.get('/user/:id', (req, res, next) => {
  console.log('although this matches')
  next()
})

app.get('/user/:id', (req, res) => {
  console.log('and this matches too')
  res.end()
})

On GET /user/42, the following is printed:
GET /user/42 上,将打印以下内容:

CALLED ONLY ONCE
although this matches
and this matches too
app.param(['id', 'page'], (req, res, next, value) => {
  console.log('CALLED ONLY ONCE with', value)
  next()
})

app.get('/user/:id/:page', (req, res, next) => {
  console.log('although this matches')
  next()
})

app.get('/user/:id/:page', (req, res) => {
  console.log('and this matches too')
  res.end()
})

On GET /user/42/3, the following is printed:
GET /user/42/3 上,将打印以下内容:

CALLED ONLY ONCE with 42
CALLED ONLY ONCE with 3
although this matches
and this matches too

app.path()

Returns the canonical path of the app, a string.
返回应用的规范路径,一个字符串。

const app = express()
const blog = express()
const blogAdmin = express()

app.use('/blog', blog)
blog.use('/admin', blogAdmin)

console.log(app.path()) // ''
console.log(blog.path()) // '/blog'
console.log(blogAdmin.path()) // '/blog/admin'

The behavior of this method can become very complicated in complex cases of mounted apps: it is usually better to use req.baseUrl to get the canonical path of the app.
在挂载应用的复杂场景中,此方法的行为可能变得非常复杂:通常更推荐使用 req.baseUrl 来获取应用的标准路径。

app.post(path, callback [, callback ...])
app.post(路径, 回调函数 [, 回调函数 ...])

Routes HTTP POST requests to the specified path with the specified callback functions. For more information, see the routing guide.
将 HTTP POST 请求路由到指定路径,并执行相应的回调函数。更多信息,请参阅路由指南。

Arguments  参数

Argument   参数 Description   描述 Default   默认值
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数数组。
  • A combination of all of the above.
    以上所有方式的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调可以调用 next('route') 来跳过剩余的路由回调。此机制可用于对路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例可参见中间件回调函数示例。

None   

Example  示例

app.post('/', (req, res) => {
  res.send('POST request to homepage')
})

app.put(path, callback [, callback ...])

Routes HTTP PUT requests to the specified path with the specified callback functions.
将 HTTP PUT 请求路由到指定路径,并使用指定的回调函数处理。

Arguments  参数

Argument   参数 Description   描述 Default   默认值
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可以是:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数数组。
  • A combination of all of the above.
    以上所有方式的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调能调用 next('route') 来跳过剩余的路由回调。此机制可用于对路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例请参见中间件回调函数示例。

None   

Example  示例

app.put('/', (req, res) => {
  res.send('PUT request to homepage')
})

app.render(view, [locals], callback)
app.render(视图, [局部变量], 回调函数)

Returns the rendered HTML of a view via the callback function. It accepts an optional parameter that is an object containing local variables for the view. It is like res.render(), except it cannot send the rendered view to the client on its own.
通过 callback 函数返回视图渲染后的 HTML。它接受一个可选参数,该参数是一个包含视图局部变量的对象。类似于 res.render(),但它无法自行将渲染后的视图发送给客户端。

Think of app.render() as a utility function for generating rendered view strings. Internally res.render() uses app.render() to render views.
可以将 app.render() 视为生成渲染视图字符串的实用函数。在内部, res.render() 使用 app.render() 来渲染视图。

The view argument performs file system operations like reading a file from disk and evaluating Node.js modules, and as so for security reasons should not contain input from the end-user.
view 参数执行文件系统操作,如从磁盘读取文件和评估 Node.js 模块,出于安全考虑,不应包含来自最终用户的输入。

The locals object is used by view engines to render a response. The object keys may be particularly sensitive and should not contain user-controlled input, as it may affect the operation of the view engine or provide a path to cross-site scripting. Consult the documentation for the used view engine for additional considerations.
locals 对象被视图引擎用于渲染响应。该对象的键可能特别敏感,不应包含用户控制的输入,因为这可能影响视图引擎的操作或提供跨站脚本的途径。请查阅所用视图引擎的文档以获取更多注意事项。

The local variable cache is reserved for enabling view cache. Set it to true, if you want to cache view during development; view caching is enabled in production by default.
局部变量 cache 保留用于启用视图缓存。在开发期间若需缓存视图,请将其设置为 true ;生产环境下默认启用视图缓存。

app.render('email', (err, html) => {
  // ...
})

app.render('email', { name: 'Tobi' }, (err, html) => {
  // ...
})

app.route(path)  app.route(路径)

Returns an instance of a single route, which you can then use to handle HTTP verbs with optional middleware. Use app.route() to avoid duplicate route names (and thus typo errors).
返回单个路由的实例,随后可用于通过可选中间件处理 HTTP 动词。使用 app.route() 以避免重复的路由名称(从而避免拼写错误)。

const app = express()

app.route('/events')
  .all((req, res, next) => {
    // runs for all HTTP verbs first
    // think of it as route specific middleware!
  })
  .get((req, res, next) => {
    res.json({})
  })
  .post((req, res, next) => {
    // maybe add a new event...
  })

app.set(name, value)  app.set(名称, 值)

Assigns setting name to value. You may store any value that you want, but certain names can be used to configure the behavior of the server. These special names are listed in the app settings table.
将设置 name 赋值为 value 。您可以存储任何所需的值,但某些名称可用于配置服务器的行为。这些特殊名称列在应用设置表中。

Calling app.set('foo', true) for a Boolean property is the same as calling app.enable('foo'). Similarly, calling app.set('foo', false) for a Boolean property is the same as calling app.disable('foo').
对布尔属性调用 app.set('foo', true) 等同于调用 app.enable('foo') 。类似地,对布尔属性调用 app.set('foo', false) 等同于调用 app.disable('foo')

Retrieve the value of a setting with app.get().
使用 app.get() 获取设置的值。

app.set('title', 'My Site')
app.get('title') // "My Site"

Application Settings  应用程序设置

The following table lists application settings.
下表列出了应用程序设置。

Note that sub-apps will:
请注意子应用将:

  • Not inherit the value of settings that have a default value. You must set the value in the sub-app.
    不继承具有默认值的设置项值。必须在子应用中设置该值。
  • Inherit the value of settings with no default value; these are explicitly noted in the table below.
    继承无默认值的设置项值;这些在下方表格中有明确标注。

Exceptions: Sub-apps will inherit the value of trust proxy even though it has a default value (for backward-compatibility); Sub-apps will not inherit the value of view cache in production (when NODE_ENV is “production”).
例外情况:子应用将继承 trust proxy 的值,尽管它有默认值(为了向后兼容);在生产环境中(当 NODE_ENV 为“production”时),子应用不会继承 view cache 的值。

Property  属性Type  类型Description  描述Default  默认值

case sensitive routing

Boolean  布尔值

Enable case sensitivity. When enabled, "/Foo" and "/foo" are different routes. When disabled, "/Foo" and "/foo" are treated the same.
启用区分大小写。启用后,“/Foo”和“/foo”被视为不同的路由。禁用时,“/Foo”和“/foo”将被视为相同。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的值。

N/A (undefined)   不适用(未定义)

env

String  字符串 Environment mode. Be sure to set to "production" in a production environment; see Production best practices: performance and reliability.
环境模式。请确保在生产环境中设置为“production”;参见生产环境最佳实践:性能与可靠性。

process.env.NODE_ENV (NODE_ENV environment variable) or “development” if NODE_ENV is not set.
process.env.NODE_ENVNODE_ENV 环境变量)或如果未设置 NODE_ENV 则为“development”。

etag

Varied  多样化

Set the ETag response header. For possible values, see the etag options table.
设置 ETag 响应头。有关可能的值,请参阅 etag 选项表。

More about the HTTP ETag header.
关于 HTTP ETag 标头的更多信息。

weak

jsonp callback name

String  字符串 Specifies the default JSONP callback name.
指定默认的 JSONP 回调名称。

“callback”

json escape

Boolean  布尔值

Enable escaping JSON responses from the res.json, res.jsonp, and res.send APIs. This will escape the characters <, >, and & as Unicode escape sequences in JSON. The purpose of this is to assist with mitigating certain types of persistent XSS attacks when clients sniff responses for HTML.
启用对来自 res.jsonres.jsonpres.send API 的 JSON 响应进行转义。这将把字符 <>& 作为 Unicode 转义序列在 JSON 中转义。此举旨在帮助缓解某些类型的持久性 XSS 攻击,当客户端嗅探响应以寻找 HTML 时。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的值。

N/A (undefined)  不适用(未定义)

json replacer

Varied  多样化的 The 'replacer' argument used by `JSON.stringify`.
`JSON.stringify`所使用的'replacer'参数。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的当前值。

N/A (undefined)   不适用(未定义)

json spaces

Varied  多样化的 The 'space' argument used by `JSON.stringify`. This is typically set to the number of spaces to use to indent prettified JSON.
`JSON.stringify`使用的'space'参数。通常设置为用于缩进美化 JSON 的空格数。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的值。

N/A (undefined)  不适用(未定义)

query parser

Varied  多样化

Disable query parsing by setting the value to false, or set the query parser to use either “simple” or “extended” or a custom query string parsing function.
通过将值设置为 false 来禁用查询解析,或者设置查询解析器使用“simple”(简单)、“extended”(扩展)或自定义查询字符串解析函数。

The simple query parser is based on Node’s native query parser, querystring.
简单查询解析器基于 Node 的原生查询解析器 querystring。

The extended query parser is based on qs.
扩展查询解析器基于 qs。

A custom query string parsing function will receive the complete query string, and must return an object of query keys and their values.
自定义查询字符串解析函数将接收完整的查询字符串,并必须返回一个包含查询键及其值的对象。

"simple"  ""simple" "

strict routing

Boolean  布尔值

Enable strict routing. When enabled, the router treats "/foo" and "/foo/" as different. Otherwise, the router treats "/foo" and "/foo/" as the same.
启用严格路由模式。启用后,路由器会将“/foo”和“/foo/”视为不同路径。否则,路由器会将“/foo”和“/foo/”视为相同路径。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的值。

N/A (undefined)   不适用(未定义)

subdomain offset

Number  数字 The number of dot-separated parts of the host to remove to access subdomain.
访问子域名需要移除的主机名中以点分隔的部分数量。
2

trust proxy

Varied  多样化的

Indicates the app is behind a front-facing proxy, and to use the X-Forwarded-* headers to determine the connection and the IP address of the client. NOTE: X-Forwarded-* headers are easily spoofed and the detected IP addresses are unreliable.
表示应用位于前端代理之后,并使用 X-Forwarded-* 头部来确定连接及客户端的 IP 地址。注意: X-Forwarded-* 头部容易被伪造,检测到的 IP 地址不可靠。

When enabled, Express attempts to determine the IP address of the client connected through the front-facing proxy, or series of proxies. The `req.ips` property, then contains an array of IP addresses the client is connected through. To enable it, use the values described in the trust proxy options table.
启用时,Express 会尝试确定通过前端代理或一系列代理连接的客户端的 IP 地址。此时,`req.ips`属性将包含客户端连接所经过的 IP 地址数组。要启用此功能,请使用信任代理选项表中描述的值。

The `trust proxy` setting is implemented using the proxy-addr package. For more information, see its documentation.
`trust proxy`设置是通过 proxy-addr 包实现的。更多信息,请参阅其文档。

NOTE: Sub-apps will inherit the value of this setting, even though it has a default value.
注意:子应用将继承此设置的值,尽管它有默认值。

false (disabled)   false (禁用)

views

String or Array  字符串或数组 A directory or an array of directories for the application's views. If an array, the views are looked up in the order they occur in the array.
应用程序视图的目录或目录数组。如果是数组,则按数组中出现的顺序查找视图。

process.cwd() + '/views'

view cache

Boolean  布尔值

Enables view template compilation caching.
启用视图模板编译缓存。

NOTE: Sub-apps will not inherit the value of this setting in production (when `NODE_ENV` is "production").
注意:在生产环境(当`NODE_ENV`为'production'时),子应用不会继承此设置的值。

true in production, otherwise undefined.
true 在生产环境中,否则为未定义。

view engine

String  字符串 The default engine extension to use when omitted.
省略时使用的默认引擎扩展。

NOTE: Sub-apps will inherit the value of this setting.
注意:子应用将继承此设置的默认值。

N/A (undefined)  不适用(未定义)

x-powered-by

Boolean  布尔值 Enables the "X-Powered-By: Express" HTTP header.
启用 'X-Powered-By: Express' HTTP 头部。

true

Options for `trust proxy` setting
`trust proxy` 设置的选项

Read Express behind proxies for more information.
阅读 Express 在代理后的配置以获取更多信息。

Type  类型Value  
Boolean  布尔值

If true, the client’s IP address is understood as the left-most entry in the X-Forwarded-* header.
如果 true ,客户端的 IP 地址将被理解为 X-Forwarded-* 标头中最左侧的条目。

If false, the app is understood as directly facing the Internet and the client’s IP address is derived from req.connection.remoteAddress. This is the default setting.
如果 false ,则该应用被视为直接面向互联网,客户端的 IP 地址将从 req.connection.remoteAddress 获取。此为默认设置。

String  字符串
String containing comma-separated values
包含逗号分隔值的字符串

Array of strings   字符串数组

An IP address, subnet, or an array of IP addresses, and subnets to trust. Pre-configured subnet names are:
一个 IP 地址、子网或 IP 地址及子网的数组,用于信任。预配置的子网名称包括:

  • loopback - 127.0.0.1/8, ::1/128
    回环地址 - 127.0.0.1/8 , ::1/128
  • linklocal - 169.254.0.0/16, fe80::/10
    链路本地地址 - 169.254.0.0/16 , fe80::/10
  • uniquelocal - 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, fc00::/7
    唯一本地地址 - 10.0.0.0/8 , 172.16.0.0/12 , 192.168.0.0/16 , fc00::/7

Set IP addresses in any of the following ways:
可通过以下任一方式设置 IP 地址:

Specify a single subnet:
指定单个子网:

app.set('trust proxy', 'loopback')

Specify a subnet and an address:
指定子网及地址:

app.set('trust proxy', 'loopback, 123.123.123.123')

Specify multiple subnets as CSV:
以 CSV 格式指定多个子网:

app.set('trust proxy', 'loopback, linklocal, uniquelocal')

Specify multiple subnets as an array:
以数组形式指定多个子网:

app.set('trust proxy', ['loopback', 'linklocal', 'uniquelocal'])

When specified, the IP addresses or the subnets are excluded from the address determination process, and the untrusted IP address nearest to the application server is determined as the client’s IP address.
当指定时,IP 地址或子网将从地址确定过程中排除,且离应用服务器最近的非受信 IP 地址将被确定为客户端的 IP 地址。

Number  数字

Trust the nth hop from the front-facing proxy server as the client.
信任来自前端代理服务器的第 n th 跳作为客户端。

Function  函数

Custom trust implementation. Use this only if you know what you are doing.
自定义信任实现。仅在您清楚操作内容时使用。

app.set('trust proxy', (ip) => {
  if (ip === '127.0.0.1' || ip === '123.123.123.123') return true // trusted IPs
  else return false
})
Options for `etag` setting
`etag` 设置的选项

NOTE: These settings apply only to dynamic files, not static files. The express.static middleware ignores these settings.
注意:这些设置仅适用于动态文件,不适用于静态文件。express.static 中间件会忽略这些设置。

The ETag functionality is implemented using the etag package. For more information, see its documentation.
ETag 功能是通过 etag 包实现的。更多信息,请参阅其文档。

Type  类型Value  
Boolean  布尔值

true enables weak ETag. This is the default setting.
true 启用弱 ETag。此为默认设置。

false disables ETag altogether.
false 完全禁用 ETag。

String  字符串 If "strong", enables strong ETag.
若设为“strong”,则启用强 ETag。

If "weak", enables weak ETag.
若设为“weak”,则启用弱 ETag。
Function  函数

Custom ETag function implementation. Use this only if you know what you are doing.
自定义 ETag 函数实现。仅在明确操作内容时使用。

app.set('etag', (body, encoding) => {
  return generateHash(body, encoding) // consider the function is defined
})

app.use([path,] callback [, callback...])
app.use([路径,] 回调函数 [, 回调函数...])

Mounts the specified middleware function or functions at the specified path: the middleware function is executed when the base of the requested path matches path.
将指定的中间件函数或函数组挂载到指定路径:当请求路径的基址匹配 path 时,执行该中间件函数。

Arguments  参数

Argument   参数 Description   描述 Default   默认
path The path for which the middleware function is invoked; can be any of:
调用中间件函数的路径;可以是以下任意一种:
  • A string representing a path.
    表示路径的字符串。
  • A path pattern.  路径模式。
  • A regular expression pattern to match paths.
    用于匹配路径的正则表达式模式。
  • An array of combinations of any of the above.
    上述任意组合的数组。
For examples, see Path examples.
示例请参见路径示例。
'/' (root path)  '/'(根路径)
callback Callback functions; can be:
回调函数;可选值包括:
  • A middleware function.  一个中间件函数。
  • A series of middleware functions (separated by commas).
    一系列中间件函数(以逗号分隔)。
  • An array of middleware functions.
    一个中间件函数数组。
  • A combination of all of the above.
    以上所有情况的组合。

You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route.
你可以提供多个行为类似于中间件的回调函数,不同的是这些回调可以调用 next('route') 来跳过剩余的路由回调。你可以利用这一机制为路由设置前置条件,若无继续当前路由的必要,则将控制权传递给后续路由。

When a callback function throws an error or returns a rejected promise, `next(err)` will be invoked automatically.
当回调函数抛出错误或返回一个被拒绝的 Promise 时,`next(err)`将自动被调用。

Since router and app implement the middleware interface, you can use them as you would any other middleware function.
由于路由器和应用实现了中间件接口,你可以像使用其他中间件函数一样使用它们。

For examples, see Middleware callback function examples.
示例可参见中间件回调函数示例。

None   

Description  描述

A route will match any path that follows its path immediately with a “/”. For example: app.use('/apple', ...) will match “/apple”, “/apple/images”, “/apple/images/news”, and so on.
一个路由会匹配任何紧随其路径后带有“ / ”的路径。例如: app.use('/apple', ...) 将匹配“/apple”、“/apple/images”、“/apple/images/news”等。

Since path defaults to “/”, middleware mounted without a path will be executed for every request to the app. For example, this middleware function will be executed for every request to the app:
由于 path 默认为“/”,未指定路径挂载的中间件将对应用的每个请求执行。例如,以下中间件函数将对应用的每个请求执行:

app.use((req, res, next) => {
  console.log('Time: %d', Date.now())
  next()
})

NOTE  注意

Sub-apps will:  子应用将:

  • Not inherit the value of settings that have a default value. You must set the value in the sub-app.
    不继承具有默认值的设置项值。必须在子应用中设置该值。
  • Inherit the value of settings with no default value.
    继承无默认值的设置项的值。

For details, see Application settings.
详情请参阅应用程序设置。

Middleware functions are executed sequentially, therefore the order of middleware inclusion is important.
中间件函数按顺序执行,因此中间件的包含顺序很重要。

// this middleware will not allow the request to go beyond it
app.use((req, res, next) => {
  res.send('Hello World')
})

// requests will never reach this route
app.get('/', (req, res) => {
  res.send('Welcome')
})

Error-handling middleware
错误处理中间件

Error-handling middleware always takes four arguments. You must provide four arguments to identify it as an error-handling middleware function. Even if you don’t need to use the next object, you must specify it to maintain the signature. Otherwise, the next object will be interpreted as regular middleware and will fail to handle errors. For details about error-handling middleware, see: Error handling.
错误处理中间件始终需要四个参数。必须提供四个参数以将其识别为错误处理中间件函数。即使不需要使用 next 对象,也必须指定它以保持签名一致。否则, next 对象将被解释为常规中间件,从而无法处理错误。有关错误处理中间件的详细信息,请参阅:错误处理。

Define error-handling middleware functions in the same way as other middleware functions, except with four arguments instead of three, specifically with the signature (err, req, res, next)):
定义错误处理中间件函数的方式与其他中间件函数相同,但需使用四个参数而非三个,具体签名为 (err, req, res, next) ):

app.use((err, req, res, next) => {
  console.error(err.stack)
  res.status(500).send('Something broke!')
})

Path examples  路径示例

The following table provides some simple examples of valid path values for mounting middleware.
下表提供了一些有效的 path 值用于挂载中间件的简单示例。

Type  类型 Example  示例
Path  路径

This will match paths starting with /abcd:
这将匹配以 /abcd 开头的路径:

app.use('/abcd', (req, res, next) => {
  next()
})
Path Pattern  路径模式

This will match paths starting with /abcd and /abd:
这将匹配以 /abcd/abd 开头的路径:

app.use('/ab{c}d', (req, res, next) => {
  next()
})
Regular Expression  正则表达式

This will match paths starting with /abc and /xyz:
这将匹配以 /abc/xyz 开头的路径:

app.use(/\/abc|\/xyz/, (req, res, next) => {
  next()
})
Array  数组

This will match paths starting with /abcd, /xyza, /lmn, and /pqr:
这将匹配以 /abcd/xyza/lmn/pqr 开头的路径:

app.use(['/abcd', '/xyza', /\/lmn|\/pqr/], (req, res, next) => {
  next()
})

Middleware callback function examples
中间件回调函数示例

The following table provides some simple examples of middleware functions that can be used as the callback argument to app.use(), app.METHOD(), and app.all().
下表提供了一些简单的中间件函数示例,这些函数可用作 callback 参数传递给 app.use()app.METHOD()app.all()

Usage  用法 Example  示例
Single Middleware  单一中间件

You can define and mount a middleware function locally.
您可以本地定义并挂载一个中间件函数。

app.use((req, res, next) => {
  next()
})

A router is valid middleware.
路由器是有效的中间件。

const router = express.Router()
router.get('/', (req, res, next) => {
  next()
})
app.use(router)

An Express app is valid middleware.
Express 应用是一个有效的中间件。

const subApp = express()
subApp.get('/', (req, res, next) => {
  next()
})
app.use(subApp)
Series of Middleware  中间件系列

You can specify more than one middleware function at the same mount path.
您可以同时为同一挂载路径指定多个中间件函数。

const r1 = express.Router()
r1.get('/', (req, res, next) => {
  next()
})

const r2 = express.Router()
r2.get('/', (req, res, next) => {
  next()
})

app.use(r1, r2)
Array  数组

Use an array to group middleware logically.
使用数组对中间件进行逻辑分组。

const r1 = express.Router()
r1.get('/', (req, res, next) => {
  next()
})

const r2 = express.Router()
r2.get('/', (req, res, next) => {
  next()
})

app.use([r1, r2])
Combination  组合

You can combine all the above ways of mounting middleware.
您可以结合上述所有挂载中间件的方式。

function mw1 (req, res, next) { next() }
function mw2 (req, res, next) { next() }

const r1 = express.Router()
r1.get('/', (req, res, next) => { next() })

const r2 = express.Router()
r2.get('/', (req, res, next) => { next() })

const subApp = express()
subApp.get('/', (req, res, next) => { next() })

app.use(mw1, [mw2, r1, r2], subApp)

Following are some examples of using the express.static middleware in an Express app.

Serve static content for the app from the “public” directory in the application directory:

// GET /style.css etc
app.use(express.static(path.join(__dirname, 'public')))

Mount the middleware at “/static” to serve static content only when their request path is prefixed with “/static”:

// GET /static/style.css etc.
app.use('/static', express.static(path.join(__dirname, 'public')))

Disable logging for static content requests by loading the logger middleware after the static middleware:

app.use(express.static(path.join(__dirname, 'public')))
app.use(logger())

Serve static files from multiple directories, but give precedence to “./public” over the others:

app.use(express.static(path.join(__dirname, 'public')))
app.use(express.static(path.join(__dirname, 'files')))
app.use(express.static(path.join(__dirname, 'uploads')))

Request

The req object represents the HTTP request and has properties for the request query string, parameters, body, HTTP headers, and so on. In this documentation and by convention, the object is always referred to as req (and the HTTP response is res) but its actual name is determined by the parameters to the callback function in which you’re working.

For example:

app.get('/user/:id', (req, res) => {
  res.send(`user ${req.params.id}`)
})

But you could just as well have:

app.get('/user/:id', (request, response) => {
  response.send(`user ${request.params.id}`)
})

The req object is an enhanced version of Node’s own request object and supports all built-in fields and methods.

Properties

In Express 4, req.files is no longer available on the req object by default. To access uploaded files on the req.files object, use multipart-handling middleware like busboy, multer, formidable, multiparty, connect-multiparty, or pez.

req.app

This property holds a reference to the instance of the Express application that is using the middleware.

If you follow the pattern in which you create a module that just exports a middleware function and require() it in your main file, then the middleware can access the Express instance via req.app

For example:

// index.js
app.get('/viewdirectory', require('./mymiddleware.js'))
// mymiddleware.js
module.exports = (req, res) => {
  res.send(`The views directory is ${req.app.get('views')}`)
}

req.baseUrl

The URL path on which a router instance was mounted.

The req.baseUrl property is similar to the mountpath property of the app object, except app.mountpath returns the matched path pattern(s).

For example:

const greet = express.Router()

greet.get('/jp', (req, res) => {
  console.log(req.baseUrl) // /greet
  res.send('Konichiwa!')
})

app.use('/greet', greet) // load the router on '/greet'

Even if you use a path pattern or a set of path patterns to load the router, the baseUrl property returns the matched string, not the pattern(s). In the following example, the greet router is loaded on two path patterns.

app.use(['/gre:"param"t', '/hel{l}o'], greet) // load the router on '/gre:"param"t' and '/hel{l}o'

When a request is made to /greet/jp, req.baseUrl is “/greet”. When a request is made to /hello/jp, req.baseUrl is “/hello”.

req.body

Contains key-value pairs of data submitted in the request body. By default, it is undefined, and is populated when you use body-parsing middleware such as express.json() or express.urlencoded().

As req.body’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.body.foo.toString() may fail in multiple ways, for example foo may not be there or may not be a string, and toString may not be a function and instead a string or other user-input.

The following example shows how to use body-parsing middleware to populate req.body.

const express = require('express')

const app = express()

app.use(express.json()) // for parsing application/json
app.use(express.urlencoded({ extended: true })) // for parsing application/x-www-form-urlencoded

app.post('/profile', (req, res, next) => {
  console.log(req.body)
  res.json(req.body)
})

req.cookies

When using cookie-parser middleware, this property is an object that contains cookies sent by the request. If the request contains no cookies, it defaults to {}.

// Cookie: name=tj
console.dir(req.cookies.name)
// => "tj"

If the cookie has been signed, you have to use req.signedCookies.

For more information, issues, or concerns, see cookie-parser.

req.fresh

When the response is still “fresh” in the client’s cache true is returned, otherwise false is returned to indicate that the client cache is now stale and the full response should be sent.

When a client sends the Cache-Control: no-cache request header to indicate an end-to-end reload request, this module will return false to make handling these requests transparent.

Further details for how cache validation works can be found in the HTTP/1.1 Caching Specification.

console.dir(req.fresh)
// => true

req.host

Contains the host derived from the Host HTTP header.

When the trust proxy setting does not evaluate to false, this property will instead get the value from the X-Forwarded-Host header field. This header can be set by the client or by the proxy.

If there is more than one X-Forwarded-Host header in the request, the value of the first header is used. This includes a single header with comma-separated values, in which the first value is used.

// Host: "example.com:3000"
console.dir(req.host)
// => 'example.com:3000'

// Host: "[::1]:3000"
console.dir(req.host)
// => '[::1]:3000'

req.hostname

Contains the hostname derived from the Host HTTP header.

When the trust proxy setting does not evaluate to false, this property will instead get the value from the X-Forwarded-Host header field. This header can be set by the client or by the proxy.

If there is more than one X-Forwarded-Host header in the request, the value of the first header is used. This includes a single header with comma-separated values, in which the first value is used.

Prior to Express v4.17.0, the X-Forwarded-Host could not contain multiple values or be present more than once.

// Host: "example.com:3000"
console.dir(req.hostname)
// => 'example.com'

req.ip

Contains the remote IP address of the request.

When the trust proxy setting does not evaluate to false, the value of this property is derived from the left-most entry in the X-Forwarded-For header. This header can be set by the client or by the proxy.

console.dir(req.ip)
// => "127.0.0.1"

req.ips

When the trust proxy setting does not evaluate to false, this property contains an array of IP addresses specified in the X-Forwarded-For request header. Otherwise, it contains an empty array. This header can be set by the client or by the proxy.

For example, if X-Forwarded-For is client, proxy1, proxy2, req.ips would be ["client", "proxy1", "proxy2"], where proxy2 is the furthest downstream.

req.method

Contains a string corresponding to the HTTP method of the request: GET, POST, PUT, and so on.

req.originalUrl

req.url is not a native Express property, it is inherited from Node’s http module.

This property is much like req.url; however, it retains the original request URL, allowing you to rewrite req.url freely for internal routing purposes. For example, the “mounting” feature of app.use() will rewrite req.url to strip the mount point.

// GET /search?q=something
console.dir(req.originalUrl)
// => "/search?q=something"

req.originalUrl is available both in middleware and router objects, and is a combination of req.baseUrl and req.url. Consider following example:

// GET 'http://www.example.com/admin/new?sort=desc'
app.use('/admin', (req, res, next) => {
  console.dir(req.originalUrl) // '/admin/new?sort=desc'
  console.dir(req.baseUrl) // '/admin'
  console.dir(req.path) // '/new'
  next()
})

req.params

This property is an object containing properties mapped to the named route “parameters”. For example, if you have the route /user/:name, then the “name” property is available as req.params.name. This object defaults to {}.

// GET /user/tj
console.dir(req.params.name)
// => "tj"

When you use a regular expression for the route definition, capture groups are provided in the array using req.params[n], where n is the nth capture group.

app.use(/^\/file\/(.*)$/, (req, res) => {
  // GET /file/javascripts/jquery.js
  console.dir(req.params[0])
  // => "javascripts/jquery.js"
})

If you need to make changes to a key in req.params, use the app.param handler. Changes are applicable only to parameters already defined in the route path.

Any changes made to the req.params object in a middleware or route handler will be reset.

Note

Express automatically decodes the values in req.params (using decodeURIComponent).

req.path

Contains the path part of the request URL.

// example.com/users?sort=desc
console.dir(req.path)
// => "/users"

When called from a middleware, the mount point is not included in req.path. See app.use() for more details.

req.protocol

Contains the request protocol string: either http or (for TLS requests) https.

When the trust proxy setting does not evaluate to false, this property will use the value of the X-Forwarded-Proto header field if present. This header can be set by the client or by the proxy.

console.dir(req.protocol)
// => "http"

req.query

This property is an object containing a property for each query string parameter in the route. When query parser is set to disabled, it is an empty object {}, otherwise it is the result of the configured query parser.

As req.query’s shape is based on user-controlled input, all properties and values in this object are untrusted and should be validated before trusting. For example, req.query.foo.toString() may fail in multiple ways, for example foo may not be there or may not be a string, and toString may not be a function and instead a string or other user-input.

The value of this property can be configured with the query parser application setting to work how your application needs it. A very popular query string parser is the qs module, and this is used by default. The qs module is very configurable with many settings, and it may be desirable to use different settings than the default to populate req.query:

const qs = require('qs')
app.set('query parser',
  (str) => qs.parse(str, { /* custom options */ }))

Check out the query parser application setting documentation for other customization options.

req.res

This property holds a reference to the response object that relates to this request object.

req.route

Contains the currently-matched route, a string. For example:

app.get('/user/{:id}', (req, res) => {
  console.dir(req.route, { depth: null })
  res.send('GET')
})

Example output from the previous snippet:

Route {
  path: '/user/{:id}',
  stack: [
    Layer {
      handle: [Function (anonymous)],
      keys: [],
      name: '<anonymous>',
      params: undefined,
      path: undefined,
      slash: false,
      matchers: [ [Function: match] ],
      method: 'get'
    }
  ],
  methods: [Object: null prototype] { get: true }
}

req.secure

A Boolean property that is true if a TLS connection is established. Equivalent to the following:

req.protocol === 'https'

req.signedCookies

When using cookie-parser middleware, this property contains signed cookies sent by the request, unsigned and ready for use. Signed cookies reside in a different object to show developer intent; otherwise, a malicious attack could be placed on req.cookie values (which are easy to spoof). Note that signing a cookie does not make it “hidden” or encrypted; but simply prevents tampering (because the secret used to sign is private).

If no signed cookies are sent, the property defaults to {}.

// Cookie: user=tobi.CP7AWaXDfAKIRfH49dQzKJx7sKzzSoPq7/AcBBRVwlI3
console.dir(req.signedCookies.user)
// => "tobi"

For more information, issues, or concerns, see cookie-parser.

req.stale

Indicates whether the request is “stale,” and is the opposite of req.fresh. For more information, see req.fresh.

console.dir(req.stale)
// => true

req.subdomains

An array of subdomains in the domain name of the request.

// Host: "tobi.ferrets.example.com"
console.dir(req.subdomains)
// => ["ferrets", "tobi"]

The application property subdomain offset, which defaults to 2, is used for determining the beginning of the subdomain segments. To change this behavior, change its value using app.set.

req.xhr

A Boolean property that is true if the request’s X-Requested-With header field is “XMLHttpRequest”, indicating that the request was issued by a client library such as jQuery.

console.dir(req.xhr)
// => true

Methods

req.accepts(types)

Checks if the specified content types are acceptable, based on the request’s Accept HTTP header field. The method returns the best match, or if none of the specified content types is acceptable, returns false (in which case, the application should respond with 406 "Not Acceptable").

The type value may be a single MIME type string (such as “application/json”), an extension name such as “json”, a comma-delimited list, or an array. For a list or array, the method returns the best match (if any).

// Accept: text/html
req.accepts('html')
// => "html"

// Accept: text/*, application/json
req.accepts('html')
// => "html"
req.accepts('text/html')
// => "text/html"
req.accepts(['json', 'text'])
// => "json"
req.accepts('application/json')
// => "application/json"

// Accept: text/*, application/json
req.accepts('image/png')
req.accepts('png')
// => false

// Accept: text/*;q=.5, application/json
req.accepts(['html', 'json'])
// => "json"

For more information, or if you have issues or concerns, see accepts.

req.acceptsCharsets(charset [, ...])

Returns the first accepted charset of the specified character sets, based on the request’s Accept-Charset HTTP header field. If none of the specified charsets is accepted, returns false.

For more information, or if you have issues or concerns, see accepts.

req.acceptsEncodings(encoding [, ...])

Returns the first accepted encoding of the specified encodings, based on the request’s Accept-Encoding HTTP header field. If none of the specified encodings is accepted, returns false.

For more information, or if you have issues or concerns, see accepts.

req.acceptsLanguages([lang, ...])

Returns the first accepted language of the specified languages, based on the request’s Accept-Language HTTP header field. If none of the specified languages is accepted, returns false.

If no lang argument is given, then req.acceptsLanguages() returns all languages from the HTTP Accept-Language header as an Array.

For more information, or if you have issues or concerns, see accepts.

Express (5.x) source: request.js line 172

Accepts (2.0) source: index.js line 195

req.get(field)

Returns the specified HTTP request header field (case-insensitive match). The Referrer and Referer fields are interchangeable.

req.get('Content-Type')
// => "text/plain"

req.get('content-type')
// => "text/plain"

req.get('Something')
// => undefined

Aliased as req.header(field).

req.is(type)

Returns the matching content type if the incoming request’s “Content-Type” HTTP header field matches the MIME type specified by the type parameter. If the request has no body, returns null. Returns false otherwise.

// With Content-Type: text/html; charset=utf-8
req.is('html') // => 'html'
req.is('text/html') // => 'text/html'
req.is('text/*') // => 'text/*'

// When Content-Type is application/json
req.is('json') // => 'json'
req.is('application/json') // => 'application/json'
req.is('application/*') // => 'application/*'

req.is('html')
// => false

For more information, or if you have issues or concerns, see type-is.

req.range(size[, options])

Range header parser.

The size parameter is the maximum size of the resource.

The options parameter is an object that can have the following properties.

Property Type Description
combine Boolean Specify if overlapping & adjacent ranges should be combined, defaults to false. When true, ranges will be combined and returned as if they were specified that way in the header.

An array of ranges will be returned or negative numbers indicating an error parsing.

  • -2 signals a malformed header string
  • -1 signals an unsatisfiable range
// parse header from request
const range = req.range(1000)

// the type of the range
if (range.type === 'bytes') {
  // the ranges
  range.forEach((r) => {
    // do something with r.start and r.end
  })
}

Response

The res object represents the HTTP response that an Express app sends when it gets an HTTP request.

In this documentation and by convention, the object is always referred to as res (and the HTTP request is req) but its actual name is determined by the parameters to the callback function in which you’re working.

For example:

app.get('/user/:id', (req, res) => {
  res.send(`user ${req.params.id}`)
})

But you could just as well have:

app.get('/user/:id', (request, response) => {
  response.send(`user ${request.params.id}`)
})

The res object is an enhanced version of Node’s own response object and supports all built-in fields and methods.

Properties

res.app

This property holds a reference to the instance of the Express application that is using the middleware.

res.app is identical to the req.app property in the request object.

res.headersSent

Boolean property that indicates if the app sent HTTP headers for the response.

app.get('/', (req, res) => {
  console.log(res.headersSent) // false
  res.send('OK')
  console.log(res.headersSent) // true
})

res.locals

Use this property to set variables accessible in templates rendered with res.render. The variables set on res.locals are available within a single request-response cycle, and will not be shared between requests.

The locals object is used by view engines to render a response. The object keys may be particularly sensitive and should not contain user-controlled input, as it may affect the operation of the view engine or provide a path to cross-site scripting. Consult the documentation for the used view engine for additional considerations.

In order to keep local variables for use in template rendering between requests, use app.locals instead.

This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on to templates rendered within the application.

app.use((req, res, next) => {
  // Make `user` and `authenticated` available in templates
  res.locals.user = req.user
  res.locals.authenticated = !req.user.anonymous
  next()
})

res.req

This property holds a reference to the request object that relates to this response object.

Methods

res.append(field [, value])

res.append() is supported by Express v4.11.0+

Appends the specified value to the HTTP response header field. If the header is not already set, it creates the header with the specified value. The value parameter can be a string or an array.

Note

calling res.set() after res.append() will reset the previously-set header value.

res.append('Link', ['<http://localhost/>', '<http://localhost:3000/>'])
res.append('Set-Cookie', 'foo=bar; Path=/; HttpOnly')
res.append('Warning', '199 Miscellaneous warning')

res.attachment([filename])

Sets the HTTP response Content-Disposition header field to “attachment”. If a filename is given, then it sets the Content-Type based on the extension name via res.type(), and sets the Content-Disposition “filename=” parameter.

res.attachment()
// Content-Disposition: attachment

res.attachment('path/to/logo.png')
// Content-Disposition: attachment; filename="logo.png"
// Content-Type: image/png

res.cookie(name, value [, options])

Sets cookie name to value. The value parameter may be a string or object converted to JSON.

The options parameter is an object that can have the following properties.

Property Type Description
domain String Domain name for the cookie. Defaults to the domain name of the app.
encode Function A synchronous function used for cookie value encoding. Defaults to encodeURIComponent.
expires Date Expiry date of the cookie in GMT. If not specified or set to 0, creates a session cookie.
httpOnly Boolean Flags the cookie to be accessible only by the web server.
maxAge Number Convenient option for setting the expiry time relative to the current time in milliseconds.
path String Path for the cookie. Defaults to “/”.
partitioned Boolean Indicates that the cookie should be stored using partitioned storage. See Cookies Having Independent Partitioned State (CHIPS) for more details.
priority String Value of the “Priority” Set-Cookie attribute.
secure Boolean Marks the cookie to be used with HTTPS only.
signed Boolean Indicates if the cookie should be signed.
sameSite Boolean or String Value of the “SameSite” Set-Cookie attribute. More information at https://tools.ietf.org/html/draft-ietf-httpbis-cookie-same-site-00#section-4.1.1.

All res.cookie() does is set the HTTP Set-Cookie header with the options provided. Any option not specified defaults to the value stated in RFC 6265.

For example:

res.cookie('name', 'tobi', { domain: '.example.com', path: '/admin', secure: true })
res.cookie('rememberme', '1', { expires: new Date(Date.now() + 900000), httpOnly: true })

You can set multiple cookies in a single response by calling res.cookie multiple times, for example:

res
  .status(201)
  .cookie('access_token', `Bearer ${token}`, {
    expires: new Date(Date.now() + 8 * 3600000) // cookie will be removed after 8 hours
  })
  .cookie('test', 'test')
  .redirect(301, '/admin')

The encode option allows you to choose the function used for cookie value encoding. Does not support asynchronous functions.

Example use case: You need to set a domain-wide cookie for another site in your organization. This other site (not under your administrative control) does not use URI-encoded cookie values.

// Default encoding
res.cookie('some_cross_domain_cookie', 'http://mysubdomain.example.com', { domain: 'example.com' })
// Result: 'some_cross_domain_cookie=http%3A%2F%2Fmysubdomain.example.com; Domain=example.com; Path=/'

// Custom encoding
res.cookie('some_cross_domain_cookie', 'http://mysubdomain.example.com', { domain: 'example.com', encode: String })
// Result: 'some_cross_domain_cookie=http://mysubdomain.example.com; Domain=example.com; Path=/;'

The maxAge option is a convenience option for setting “expires” relative to the current time in milliseconds. The following is equivalent to the second example above.

res.cookie('rememberme', '1', { maxAge: 900000, httpOnly: true })

You can pass an object as the value parameter; it is then serialized as JSON and parsed by bodyParser() middleware.

res.cookie('cart', { items: [1, 2, 3] })
res.cookie('cart', { items: [1, 2, 3] }, { maxAge: 900000 })

When using cookie-parser middleware, this method also supports signed cookies. Simply include the signed option set to true. Then, res.cookie() will use the secret passed to cookieParser(secret) to sign the value.

res.cookie('name', 'tobi', { signed: true })

Later, you may access this value through the req.signedCookies object.

res.clearCookie(name [, options])

Clears the cookie specified by name. For details about the options object, see res.cookie().

Web browsers and other compliant clients will only clear the cookie if the given options is identical to those given to res.cookie(), excluding expires and maxAge.

res.cookie('name', 'tobi', { path: '/admin' })
res.clearCookie('name', { path: '/admin' })

res.download(path [, filename] [, options] [, fn])

The optional options argument is supported by Express v4.16.0 onwards.

Transfers the file at path as an “attachment”. Typically, browsers will prompt the user for download. By default, the Content-Disposition header “filename=” parameter is derived from the path argument, but can be overridden with the filename parameter. If path is relative, then it will be based on the current working directory of the process or the root option, if provided.

This API provides access to data on the running file system. Ensure that either (a) the way in which the path argument was constructed is secure if it contains user input or (b) set the root option to the absolute path of a directory to contain access within.

When the root option is provided, Express will validate that the relative path provided as path will resolve within the given root option.

The following table provides details on the options parameter.

The optional options argument is supported by Express v4.16.0 onwards.

Property Description Default Availability
maxAge Sets the max-age property of the Cache-Control header in milliseconds or a string in ms format 0 4.16+
root Root directory for relative filenames.   4.18+
lastModified Sets the Last-Modified header to the last modified date of the file on the OS. Set false to disable it. Enabled 4.16+
headers Object containing HTTP headers to serve with the file. The header Content-Disposition will be overridden by the filename argument.   4.16+
dotfiles Option for serving dotfiles. Possible values are “allow”, “deny”, “ignore”. “ignore” 4.16+
acceptRanges Enable or disable accepting ranged requests. true 4.16+
cacheControl Enable or disable setting Cache-Control response header. true 4.16+
immutable Enable or disable the immutable directive in the Cache-Control response header. If enabled, the maxAge option should also be specified to enable caching. The immutable directive will prevent supported clients from making conditional requests during the life of the maxAge option to check if the file has changed. false 4.16+

The method invokes the callback function fn(err) when the transfer is complete or when an error occurs. If the callback function is specified and an error occurs, the callback function must explicitly handle the response process either by ending the request-response cycle, or by passing control to the next route.

res.download('/report-12345.pdf')

res.download('/report-12345.pdf', 'report.pdf')

res.download('/report-12345.pdf', 'report.pdf', (err) => {
  if (err) {
    // Handle error, but keep in mind the response may be partially-sent
    // so check res.headersSent
  } else {
    // decrement a download credit, etc.
  }
})

res.end([data[, encoding]][, callback])

Ends the response process. This method actually comes from Node core, specifically the response.end() method of http.ServerResponse.

Use to quickly end the response without any data. If you need to respond with data, instead use methods such as res.send() and res.json().

res.end()
res.status(404).end()

res.format(object)

Performs content-negotiation on the Accept HTTP header on the request object, when present. It uses req.accepts() to select a handler for the request, based on the acceptable types ordered by their quality values. If the header is not specified, the first callback is invoked. When no match is found, the server responds with 406 “Not Acceptable”, or invokes the default callback.

The Content-Type response header is set when a callback is selected. However, you may alter this within the callback using methods such as res.set() or res.type().

The following example would respond with { "message": "hey" } when the Accept header field is set to “application/json” or “*/json” (however, if it is “*/*”, then the response will be “hey”).

res.format({
  'text/plain' () {
    res.send('hey')
  },

  'text/html' () {
    res.send('<p>hey</p>')
  },

  'application/json' () {
    res.send({ message: 'hey' })
  },

  default () {
    // log the request and respond with 406
    res.status(406).send('Not Acceptable')
  }
})

In addition to canonicalized MIME types, you may also use extension names mapped to these types for a slightly less verbose implementation:

res.format({
  text () {
    res.send('hey')
  },

  html () {
    res.send('<p>hey</p>')
  },

  json () {
    res.send({ message: 'hey' })
  }
})

res.get(field)

Returns the HTTP response header specified by field. The match is case-insensitive.

res.get('Content-Type')
// => "text/plain"

res.json([body])

Sends a JSON response. This method sends a response (with the correct content-type) that is the parameter converted to a JSON string using JSON.stringify().

The parameter can be any JSON type, including object, array, string, Boolean, number, or null, and you can also use it to convert other values to JSON.

res.json(null)
res.json({ user: 'tobi' })
res.status(500).json({ error: 'message' })

res.jsonp([body])

Sends a JSON response with JSONP support. This method is identical to res.json(), except that it opts-in to JSONP callback support.

res.jsonp(null)
// => callback(null)

res.jsonp({ user: 'tobi' })
// => callback({ "user": "tobi" })

res.status(500).jsonp({ error: 'message' })
// => callback({ "error": "message" })

By default, the JSONP callback name is simply callback. Override this with the jsonp callback name setting.

The following are some examples of JSONP responses using the same code:

// ?callback=foo
res.jsonp({ user: 'tobi' })
// => foo({ "user": "tobi" })

app.set('jsonp callback name', 'cb')

// ?cb=foo
res.status(500).jsonp({ error: 'message' })
// => foo({ "error": "message" })

Joins the links provided as properties of the parameter to populate the response’s Link HTTP header field.

For example, the following call:

res.links({
  next: 'http://api.example.com/users?page=2',
  last: 'http://api.example.com/users?page=5'
})

Yields the following results:

Link: <http://api.example.com/users?page=2>; rel="next",
      <http://api.example.com/users?page=5>; rel="last"

res.location(path)

Sets the response Location HTTP header to the specified path parameter.

res.location('/foo/bar')
res.location('http://example.com')

After encoding the URL, if not encoded already, Express passes the specified URL to the browser in the Location header, without any validation.

Browsers take the responsibility of deriving the intended URL from the current URL or the referring URL, and the URL specified in the Location header; and redirect the user accordingly.

res.redirect([status,] path)

Redirects to the URL derived from the specified path, with specified status, a positive integer that corresponds to an HTTP status code. If not specified, status defaults to 302 "Found".

res.redirect('/foo/bar')
res.redirect('http://example.com')
res.redirect(301, 'http://example.com')
res.redirect('../login')

Redirects can be a fully-qualified URL for redirecting to a different site:

res.redirect('http://google.com')

Redirects can be relative to the root of the host name. For example, if the application is on http://example.com/admin/post/new, the following would redirect to the URL http://example.com/admin:

res.redirect('/admin')

Redirects can be relative to the current URL. For example, from http://example.com/blog/admin/ (notice the trailing slash), the following would redirect to the URL http://example.com/blog/admin/post/new.

res.redirect('post/new')

Redirecting to post/new from http://example.com/blog/admin (no trailing slash), will redirect to http://example.com/blog/post/new.

If you found the above behavior confusing, think of path segments as directories (with trailing slashes) and files, it will start to make sense.

Path-relative redirects are also possible. If you were on http://example.com/admin/post/new, the following would redirect to http://example.com/admin/post:

res.redirect('..')

See also Security best practices: Prevent open redirect vulnerabilities.

res.render(view [, locals] [, callback])

Renders a view and sends the rendered HTML string to the client. Optional parameters:

  • locals, an object whose properties define local variables for the view.
  • callback, a callback function. If provided, the method returns both the possible error and rendered string, but does not perform an automated response. When an error occurs, the method invokes next(err) internally.

The view argument is a string that is the file path of the view file to render. This can be an absolute path, or a path relative to the views setting. If the path does not contain a file extension, then the view engine setting determines the file extension. If the path does contain a file extension, then Express will load the module for the specified template engine (via require()) and render it using the loaded module’s __express function.

For more information, see Using template engines with Express.

Warning

The view argument performs file system operations like reading a file from disk and evaluating Node.js modules, and as so for security reasons should not contain input from the end-user.

Warning

The locals object is used by view engines to render a response. The object keys may be particularly sensitive and should not contain user-controlled input, as it may affect the operation of the view engine or provide a path to cross-site scripting. Consult the documentation for the used view engine for additional considerations.

Caution

The local variable cache enables view caching. Set it to true, to cache the view during development; view caching is enabled in production by default.

// send the rendered view to the client
res.render('index')

// if a callback is specified, the rendered HTML string has to be sent explicitly
res.render('index', (err, html) => {
  res.send(html)
})

// pass a local variable to the view
res.render('user', { name: 'Tobi' }, (err, html) => {
  // ...
})

res.send([body])

Sends the HTTP response.

The body parameter can be a Buffer object, a String, an object, Boolean, or an Array. For example:

res.send(Buffer.from('whoop'))
res.send({ some: 'json' })
res.send('<p>some html</p>')
res.status(404).send('Sorry, we cannot find that!')
res.status(500).send({ error: 'something blew up' })

This method performs many useful tasks for simple non-streaming responses: For example, it automatically assigns the Content-Length HTTP response header field and provides automatic HEAD and HTTP cache freshness support.

When the parameter is a Buffer object, the method sets the Content-Type response header field to “application/octet-stream”, unless previously defined as shown below:

res.set('Content-Type', 'text/html')
res.send(Buffer.from('<p>some html</p>'))

When the parameter is a String, the method sets the Content-Type to “text/html”:

res.send('<p>some html</p>')

When the parameter is an Array or Object, Express responds with the JSON representation:

res.send({ user: 'tobi' })
res.send([1, 2, 3])

res.sendFile(path [, options] [, fn])

res.sendFile() is supported by Express v4.8.0 onwards.

Transfers the file at the given path. Sets the Content-Type response HTTP header field based on the filename’s extension. Unless the root option is set in the options object, path must be an absolute path to the file.

This API provides access to data on the running file system. Ensure that either (a) the way in which the path argument was constructed into an absolute path is secure if it contains user input or (b) set the root option to the absolute path of a directory to contain access within.

When the root option is provided, the path argument is allowed to be a relative path, including containing ... Express will validate that the relative path provided as path will resolve within the given root option.

The following table provides details on the options parameter.

Property Description Default Availability
maxAge Sets the max-age property of the Cache-Control header in milliseconds or a string in ms format 0  
root Root directory for relative filenames.    
lastModified Sets the Last-Modified header to the last modified date of the file on the OS. Set false to disable it. Enabled 4.9.0+
headers Object containing HTTP headers to serve with the file.    
dotfiles Option for serving dotfiles. Possible values are “allow”, “deny”, “ignore”. “ignore”  
acceptRanges Enable or disable accepting ranged requests. true 4.14+
cacheControl Enable or disable setting Cache-Control response header. true 4.14+
immutable Enable or disable the immutable directive in the Cache-Control response header. If enabled, the maxAge option should also be specified to enable caching. The immutable directive will prevent supported clients from making conditional requests during the life of the maxAge option to check if the file has changed. false 4.16+

The method invokes the callback function fn(err) when the transfer is complete or when an error occurs. If the callback function is specified and an error occurs, the callback function must explicitly handle the response process either by ending the request-response cycle, or by passing control to the next route.

Here is an example of using res.sendFile with all its arguments.

app.get('/file/:name', (req, res, next) => {
  const options = {
    root: path.join(__dirname, 'public'),
    dotfiles: 'deny',
    headers: {
      'x-timestamp': Date.now(),
      'x-sent': true
    }
  }

  const fileName = req.params.name
  res.sendFile(fileName, options, (err) => {
    if (err) {
      next(err)
    } else {
      console.log('Sent:', fileName)
    }
  })
})

The following example illustrates using res.sendFile to provide fine-grained support for serving files:

app.get('/user/:uid/photos/:file', (req, res) => {
  const uid = req.params.uid
  const file = req.params.file

  req.user.mayViewFilesFrom(uid, (yes) => {
    if (yes) {
      res.sendFile(`/uploads/${uid}/${file}`)
    } else {
      res.status(403).send("Sorry! You can't see that.")
    }
  })
})

For more information, or if you have issues or concerns, see send.

res.sendStatus(statusCode)

Sets the response HTTP status code to statusCode and sends the registered status message as the text response body. If an unknown status code is specified, the response body will just be the code number.

res.sendStatus(404)

Some versions of Node.js will throw when res.statusCode is set to an invalid HTTP status code (outside of the range 100 to 599). Consult the HTTP server documentation for the Node.js version being used.

More about HTTP Status Codes

res.set(field [, value])

Sets the response’s HTTP header field to value. To set multiple fields at once, pass an object as the parameter.

res.set('Content-Type', 'text/plain')

res.set({
  'Content-Type': 'text/plain',
  'Content-Length': '123',
  ETag: '12345'
})

Aliased as res.header(field [, value]).

res.status(code)

Sets the HTTP status for the response. It is a chainable alias of Node’s response.statusCode.

res.status(403).end()
res.status(400).send('Bad Request')
res.status(404).sendFile('/absolute/path/to/404.png')

res.type(type)

Sets the Content-Type HTTP header to the MIME type as determined by the specified type. If type contains the “/” character, then it sets the Content-Type to the exact value of type, otherwise it is assumed to be a file extension and the MIME type is looked up using the contentType() method of the mime-types package.

res.type('.html') // => 'text/html'
res.type('html') // => 'text/html'
res.type('json') // => 'application/json'
res.type('application/json') // => 'application/json'
res.type('png') // => image/png:

Aliased as res.contentType(type).

res.vary(field)

Adds the field to the Vary response header, if it is not there already.

res.vary('User-Agent').render('docs')

Router

A router object is an instance of middleware and routes. You can think of it as a “mini-application,” capable only of performing middleware and routing functions. Every Express application has a built-in app router.

A router behaves like middleware itself, so you can use it as an argument to app.use() or as the argument to another router’s use() method.

The top-level express object has a Router() method that creates a new router object.

Once you’ve created a router object, you can add middleware and HTTP method routes (such as get, put, post, and so on) to it just like an application. For example:

// invoked for any requests passed to this router
router.use((req, res, next) => {
  // .. some logic here .. like any other middleware
  next()
})

// will handle any request that ends in /events
// depends on where the router is "use()'d"
router.get('/events', (req, res, next) => {
  // ..
})

You can then use a router for a particular root URL in this way separating your routes into files or even mini-apps.

// only requests to /calendar/* will be sent to our "router"
app.use('/calendar', router)

Keep in mind that any middleware applied to a router will run for all requests on that router’s path, even those that aren’t part of the router.

Methods

router.all(path, [callback, ...] callback)

This method is just like the router.METHOD() methods, except that it matches all HTTP methods (verbs).

This method is extremely useful for mapping “global” logic for specific path prefixes or arbitrary matches. For example, if you placed the following route at the top of all other route definitions, it would require that all routes from that point on would require authentication, and automatically load a user. Keep in mind that these callbacks do not have to act as end points; loadUser can perform a task, then call next() to continue matching subsequent routes.

router.all('{*splat}', requireAuthentication, loadUser)

Or the equivalent:

router.all('{*splat}', requireAuthentication)
router.all('{*splat}', loadUser)

Another example of this is white-listed “global” functionality. Here, the example is much like before, but it only restricts paths prefixed with “/api”:

router.all('/api/{*splat}', requireAuthentication)

router.METHOD(path, [callback, ...] callback)

The router.METHOD() methods provide the routing functionality in Express, where METHOD is one of the HTTP methods, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are router.get(), router.post(), router.put(), and so on.

The router.get() function is automatically called for the HTTP HEAD method in addition to the GET method if router.head() was not called for the path before router.get().

You can provide multiple callbacks, and all are treated equally, and behave just like middleware, except that these callbacks may invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to perform pre-conditions on a route then pass control to subsequent routes when there is no reason to proceed with the route matched.

The following snippet illustrates the most simple route definition possible. Express translates the path strings to regular expressions, used internally to match incoming requests. Query strings are not considered when performing these matches, for example “GET /” would match the following route, as would “GET /?name=tobi”.

router.get('/', (req, res) => {
  res.send('hello world')
})

You can also use regular expressions—useful if you have very specific constraints, for example the following would match “GET /commits/71dbb9c” as well as “GET /commits/71dbb9c..4c084f9”.

router.get(/^\/commits\/(\w+)(?:\.\.(\w+))?$/, (req, res) => {
  const from = req.params[0]
  const to = req.params[1] || 'HEAD'
  res.send(`commit range ${from}..${to}`)
})

You can use next primitive to implement a flow control between different middleware functions, based on a specific program state. Invoking next with the string 'router' will cause all the remaining route callbacks on that router to be bypassed.

The following example illustrates next('router') usage.

function fn (req, res, next) {
  console.log('I come here')
  next('router')
}
router.get('/foo', fn, (req, res, next) => {
  console.log('I dont come here')
})
router.get('/foo', (req, res, next) => {
  console.log('I dont come here')
})
app.get('/foo', (req, res) => {
  console.log(' I come here too')
  res.end('good')
})

router.param(name, callback)

Adds callback triggers to route parameters, where name is the name of the parameter and callback is the callback function. Although name is technically optional, using this method without it is deprecated starting with Express v4.11.0 (see below).

The parameters of the callback function are:

  • req, the request object.
  • res, the response object.
  • next, indicating the next middleware function.
  • The value of the name parameter.
  • The name of the parameter.

Unlike app.param(), router.param() does not accept an array of route parameters.

For example, when :user is present in a route path, you may map user loading logic to automatically provide req.user to the route, or perform validations on the parameter input.

router.param('user', (req, res, next, id) => {
  // try to get the user details from the User model and attach it to the request object
  User.find(id, (err, user) => {
    if (err) {
      next(err)
    } else if (user) {
      req.user = user
      next()
    } else {
      next(new Error('failed to load user'))
    }
  })
})

Param callback functions are local to the router on which they are defined. They are not inherited by mounted apps or routers, nor are they triggered for route parameters inherited from parent routers. Hence, param callbacks defined on router will be triggered only by route parameters defined on router routes.

A param callback will be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples.

router.param('id', (req, res, next, id) => {
  console.log('CALLED ONLY ONCE')
  next()
})

router.get('/user/:id', (req, res, next) => {
  console.log('although this matches')
  next()
})

router.get('/user/:id', (req, res) => {
  console.log('and this matches too')
  res.end()
})

On GET /user/42, the following is printed:

CALLED ONLY ONCE
although this matches
and this matches too

router.route(path)

Returns an instance of a single route which you can then use to handle HTTP verbs with optional middleware. Use router.route() to avoid duplicate route naming and thus typing errors.

Building on the router.param() example above, the following code shows how to use router.route() to specify various HTTP method handlers.

const router = express.Router()

router.param('user_id', (req, res, next, id) => {
  // sample user, would actually fetch from DB, etc...
  req.user = {
    id,
    name: 'TJ'
  }
  next()
})

router.route('/users/:user_id')
  .all((req, res, next) => {
  // runs for all HTTP verbs first
  // think of it as route specific middleware!
    next()
  })
  .get((req, res, next) => {
    res.json(req.user)
  })
  .put((req, res, next) => {
  // just an example of maybe updating the user
    req.user.name = req.params.name
    // save user ... etc
    res.json(req.user)
  })
  .post((req, res, next) => {
    next(new Error('not implemented'))
  })
  .delete((req, res, next) => {
    next(new Error('not implemented'))
  })

This approach re-uses the single /users/:user_id path and adds handlers for various HTTP methods.

Note

When you use router.route(), middleware ordering is based on when the route is created, not when method handlers are added to the route. For this purpose, you can consider method handlers to belong to the route to which they were added.

router.use([path], [function, ...] function)

Uses the specified middleware function or functions, with optional mount path path, that defaults to “/”.

This method is similar to app.use(). A simple example and use case is described below. See app.use() for more information.

Middleware is like a plumbing pipe: requests start at the first middleware function defined and work their way “down” the middleware stack processing for each path they match.

const express = require('express')
const app = express()
const router = express.Router()

// simple logger for this router's requests
// all requests to this router will first hit this middleware
router.use((req, res, next) => {
  console.log('%s %s %s', req.method, req.url, req.path)
  next()
})

// this will only be invoked if the path starts with /bar from the mount point
router.use('/bar', (req, res, next) => {
  // ... maybe some additional /bar logging ...
  next()
})

// always invoked
router.use((req, res, next) => {
  res.send('Hello World')
})

app.use('/foo', router)

app.listen(3000)

The “mount” path is stripped and is not visible to the middleware function. The main effect of this feature is that a mounted middleware function may operate without code changes regardless of its “prefix” pathname.

The order in which you define middleware with router.use() is very important. They are invoked sequentially, thus the order defines middleware precedence. For example, usually a logger is the very first middleware you would use, so that every request gets logged.

const logger = require('morgan')

router.use(logger())
router.use(express.static(path.join(__dirname, 'public')))
router.use((req, res) => {
  res.send('Hello')
})

Now suppose you wanted to ignore logging requests for static files, but to continue logging routes and middleware defined after logger(). You would simply move the call to express.static() to the top, before adding the logger middleware:

router.use(express.static(path.join(__dirname, 'public')))
router.use(logger())
router.use((req, res) => {
  res.send('Hello')
})

Another example is serving files from multiple directories, giving precedence to “./public” over the others:

app.use(express.static(path.join(__dirname, 'public')))
app.use(express.static(path.join(__dirname, 'files')))
app.use(express.static(path.join(__dirname, 'uploads')))

The router.use() method also supports named parameters so that your mount points for other routers can benefit from preloading using named parameters.

NOTE: Although these middleware functions are added via a particular router, when they run is defined by the path they are attached to (not the router). Therefore, middleware added via one router may run for other routers if its routes match. For example, this code shows two different routers mounted on the same path:

const authRouter = express.Router()
const openRouter = express.Router()

authRouter.use(require('./authenticate').basic(usersdb))

authRouter.get('/:user_id/edit', (req, res, next) => {
  // ... Edit user UI ...
})
openRouter.get('/', (req, res, next) => {
  // ... List users ...
})
openRouter.get('/:user_id', (req, res, next) => {
  // ... View user ...
})

app.use('/users', authRouter)
app.use('/users', openRouter)

Even though the authentication middleware was added via the authRouter it will run on the routes defined by the openRouter as well since both routers were mounted on /users. To avoid this behavior, use different paths for each router.

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