Is it necessary to escape the replacement string in a String.replace() call with a regular expression?

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##\";
         


        

Answer 1

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 nth parenthesized submatch string, provided the first argument was a RegExp object.

Answer 2

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);