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g3rv4
Asked: 2020-05-30 04:52:57 +0800 CST 2020-05-30 04:52:57 +0800 CST

Replace a part of the string without magic

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I have the following code:

text = 'check this regex<placeholder>, it will do what you want';
result = text.replace('<placeholder>', ' `^sql$`');

console.log(result);

As you can see, the result is

check this regex `^sqlcheck this regex, it will do what you want

when i would expect it to be

check this regex `^sql$`, it will do what you want

Why is this happening? and... how can I fix it?

javascript

1 Answers

  1. Best Answer

    The function replacehas an interesting behavior regarding the second parameter : (bolds are mine).

    The replacement string can include the following special replacement patterns:

    Pattern Inserts

    • $$ Inserts a "$".
    • $& Inserts the matched substring.
    • $` Inserts the portion of the string that precedes the matched substring.
    • $' Inserts the portion of the string that follows the matched substring.
    • $n Where n is a positive integer less than 100, inserts the nth parenthesized submatch string, provided the first argument was a RegExp object. Note that this is 1-indexed.

    Approximate translation:

    The replacement string can include the following replacement patterns:

    • $$insert a "$".
    • $&Inserts the substring that matches the search.
    • $`Inserts the portion of the string that precedes the substring that matches the search.
    • $'Inserts the portion of the string that follows the substring that matches the search.
    • $nWhere n is a positive integer and less than 100, insert the nth sub-match in parentheses (capture group), assuming the pattern (first parameter) is a regular expression.

    That is, in this case it is added ^sqland after this the entire string that precedes the match is added . It can be fixed by doubling the $ character:

    const text = 'check this regex<placeholder>, it will do what you want';
const result = text.replace('<placeholder>', ' `^sql$$`');
//                                                  ^^
console.log(result);

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