Why Does `text.replace(text, \'$\\\'\')` Result in an Empty String in JavaScript?

Unexpected Behavior in String Replacement Using $ Symbol

A puzzling issue arises when using the string.replace() method for string replacement, particularly when the replacement string contains the $ symbol. Consider the following code:

<code class="javascript">var text = "as";
text = text.replace(text,"$\'");
console.log(text);</code>

This code results in an empty string being printed to the console, which may seem counterintuitive. To understand this behavior, it is crucial to comprehend the special significance of $ in JavaScript Regular Expressions and the string.replace() method.

According to the Mozilla Developer Network documentation, $ has a special meaning in regular expressions. Within a regular expression, $ is typically used to mark the end of the string being matched. However, when used in the replacement string for string.replace() method, $ represents the entire matched pattern, or capture group.

In this case, since text itself is getting replaced with $' where $ resolves to the matched pattern (which is as), the resultant string becomes $as and further replacing as with $ resolves to empty string.

To resolve the issue, it is recommended to escape the $ character if you intend to use it as a literal character within the replacement string. One solution is to use $$ as the replacement string.

<code class="javascript">var text = "as";
text = text.replace(text,"$$\'");
console.log(text); // Outputs: $'</code>

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