是否有必要使用正则表达式转义String.replace（）调用中的替换字符串？

Question

In wonder if it is necessary to escape certain chars in the replacement string of a replace operation in Javascript. What I have is this:

let t = "##links##";
let t2 = t.replace(/##links##/, `{"labels": ["'$'"]}`);
console.log(t2);

The console output is:

{"labels": ["'"]}

which is pretty surprising. However, I cannot find anything in the documentation that suggests to escape the replacement string. So, what's going on here?

Answer 1

You need to double the $ symbol to replace with a literal $ :

 let t = "##links##"; let t2 = t.replace(/##links##/, `{"labels": ["'$$'"]}`); console.log(t2); 

See Specifying a string as a parameter listing all the possible "special" combinations inside a regex replacement part.

If you check that table, you will see that $ starts the "special" sequences. Thus, it should be escaped in some way. In JS, a dollar is used to escape the literal dollar symbol. $& is a backreference to the whole match, $` inserts the portion of the string that precedes the matched substring, $' inserts the portion of the string that follows the matched substring. $n is a backrefernece to Group n .

So, if you have a dynamic, user-defined replacement string that is not supposed to have backreferences, you may use

 let t = "##links##"; let rep = `{"labels": ["'$'"]}`; let t2 = t.replace(/##links##/, rep.replace(/\\$/g, '$$$$')); console.log(t2); 

Answer 2

Dollar sign ( $ ) is special in replace . If you want a single, literal dollar sign, use $$ . Otherwise, the replacement string can include the following special replacement patterns :

• $$ 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 n th parenthesized submatch string, provided the first argument was a RegExp object.