Add Space Before Match

2024年6月21日

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while ((match = regex.exec(text)) !== null) { if(match[1]){ console.log(match); let oldV = match[0]; let index = match.index; // 拿到字符串index的上一个 let pre = text[index - 1]; if(pre !== ' '){ // 添加一个空格 } }

To complete the code, you need to implement the logic for adding a space before oldV if the character before it is not a space. Here's the updated code snippet:

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    if (match[1]) {
        console.log(match);
        let oldV = match[0];
        let index = match.index;
        // Get the character before the index
        let pre = text[index - 1];
        
        if (pre !== ' ') {
            // Add a space before the match
            text = text.slice(0, index) + ' ' + text.slice(index);
            // Adjust regex lastIndex due to insertion of a new character
            regex.lastIndex++;
        }
    }
}

console.log(text);

In this code:

text is your input string.
regex is your regular expression pattern.
match is the result of executing the regex on the text.
Inside the while loop, you check if match[1] exists.
oldV stores the matched string, and index stores the position of the match in the text.
The character before the match is obtained and stored in pre.
If pre is not a space, a space is added before the match using string slicing.
The regex.lastIndex is incremented to account for the insertion of the new character, ensuring the regex continues to search correctly.

if(match[1]){ let index = match.index; // 拿到字符串index的上一个 let pre = text[index - 1]; if(pre !== ' '){ // 添加一个空格 // Add a space before the match text = text.slice(0, index) + ' ' + text.slice(index); // Adjust regex lastIndex due to insertion of a new character regex.lastIndex++; } }else{ // 针对$$ let index = match.index; // 拿到字符串index的上一个 let pre = text[index - 1]; text = text.slice(0, index) + '\n' + text.slice(index); // 在最后加一个\n }

Here's the complete code that handles both cases: adding a space before a match when the preceding character is not a space, and adding a newline character before $$:

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    let index = match.index;
    // Get the character before the index
    let pre = text[index - 1];

    if (match[1]) {
        if (pre !== ' ') {
            // Add a space before the match
            text = text.slice(0, index) + ' ' + text.slice(index);
            // Adjust regex lastIndex due to insertion of a new character
            regex.lastIndex++;
        }
    } else {
        // Handle case for $$
        text = text.slice(0, index) + '\n' + text.slice(index);
        // Adjust regex lastIndex due to insertion of a new character
        regex.lastIndex++;
    }
}

console.log(text);

Explanation:

The code initializes the text and regex variables.
It runs a while loop to process each match found by the regular expression.
For each match, it determines the character before the match's index.
If the match has a group (indicated by match[1]), it checks if the preceding character is a space. If not, it adds a space before the match.
If the match does not have a group (indicating it is $$), it adds a newline character before the match.
The regex.lastIndex is adjusted in both cases to account for the insertion of the new character, ensuring the regex continues to search correctly.

// 在最后加一个\n

Got it. You want to add a newline character at the end of the string if the match is $$. Here's the updated code:

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    let index = match.index;
    // Get the character before the index
    let pre = text[index - 1];

    if (match[1]) {
        if (pre !== ' ') {
            // Add a space before the match
            text = text.slice(0, index) + ' ' + text.slice(index);
            // Adjust regex lastIndex due to insertion of a new character
            regex.lastIndex++;
        }
    } else {
        // Handle case for $$
        text = text.slice(0, index) + '\n' + text.slice(index);
        // Adjust regex lastIndex due to insertion of a new character
        regex.lastIndex++;
    }
}

// Add a newline character at the end
text += '\n';

console.log(text);

In this code, after processing all matches, we add a newline character at the end of the string by using text += '\n';. This ensures that if any match was $$, the final string ends with a newline.

。。。你看一下我的注释

我明白了，你的注释是想在处理 $$ 的情况下，在最后再加一个 \n。下面是根据你的注释修改后的完整代码：

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    let index = match.index;
    // 拿到字符串index的上一个字符
    let pre = text[index - 1];

    if (match[1]) {
        if (pre !== ' ') {
            // 添加一个空格
            text = text.slice(0, index) + ' ' + text.slice(index);
            // 调整regex.lastIndex由于插入了一个新的字符
            regex.lastIndex++;
        }
    } else {
        // 针对$$的处理
        text = text.slice(0, index) + '\n' + text.slice(index);
        // 调整regex.lastIndex由于插入了一个新的字符
        regex.lastIndex++;
    }
}

// 在最后加一个\n
text += '\n';

console.log(text);

在这个代码中，最后一行 text += '\n'; 确保无论是否匹配到 $$，最后都会在字符串末尾添加一个换行符。这符合你注释中的要求。

啊啊啊啊啊你看我注释的位置啊else{ // 针对$$ let index = match.index; // 拿到字符串index的上一个 let pre = text[index - 1]; text = text.slice(0, index) + '\n' + text.slice(index); // 在最后加一个\n }

明白了，你是希望在匹配到 $$ 的情况下，在匹配位置前添加一个换行符，并在字符串的最后也添加一个换行符。下面是更新后的代码：

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    let index = match.index;
    // 拿到字符串index的上一个字符
    let pre = text[index - 1];

    if (match[1]) {
        if (pre !== ' ') {
            // 添加一个空格
            text = text.slice(0, index) + ' ' + text.slice(index);
            // 调整regex.lastIndex由于插入了一个新的字符
            regex.lastIndex++;
        }
    } else {
        // 针对$$的处理
        text = text.slice(0, index) + '\n' + text.slice(index);
        // 调整regex.lastIndex由于插入了一个新的字符
        regex.lastIndex++;
    }
}

// 在最后加一个\n
text += '\n';

console.log(text);

这个代码在匹配到 $$ 的情况下，会在匹配位置前添加一个换行符，并且在循环结束后在字符串的末尾添加一个换行符。

额。。。在else里面我不但要改动第一个位置我还要改动index+字符串长度

明白了，你希望在匹配到 $$ 的情况下，在匹配位置前添加一个换行符，并且在匹配到的字符串后再添加一个换行符。下面是更新后的代码：

javascript
let text = "your text here";
let regex = /your_regex_pattern/g;
let match;

while ((match = regex.exec(text)) !== null) {
    let index = match.index;
    // 拿到字符串index的上一个字符
    let pre = text[index - 1];

    if (match[1]) {
        if (pre !== ' ') {
            // 添加一个空格
            text = text.slice(0, index) + ' ' + text.slice(index);
            // 调整regex.lastIndex由于插入了一个新的字符
            regex.lastIndex++;
        }
    } else {
        // 针对$$的处理
        let matchLength = match[0].length;
        text = text.slice(0, index) + '\n' + text.slice(index, index + matchLength) + '\n' + text.slice(index + matchLength);
        // 调整regex.lastIndex由于插入了新的字符
        regex.lastIndex += 2; // 插入了两个换行符
    }
}

console.log(text);

在这个代码中：

如果匹配到 $$（即 else 块中的情况），首先在匹配位置前添加一个换行符。
然后在匹配到的字符串后也添加一个换行符。
最后调整 regex.lastIndex，以确保正则表达式继续搜索时位置正确。

这样，在每次匹配到 $$ 的情况下，会在前后各添加一个换行符。

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