Why does `string.replace` with a dollar sign ($) as the replacement result in an empty string in JavaScript?

Unexpected Behavior of string.replace with Dollar Sign ($) Replacement

In JavaScript, the string.replace method offers a convenient way to substitute substrings within a string. However, when using the dollar sign ($) as a replacement string, unexpected behavior may arise.

Consider the following code snippet:

var text = "as";
text = text.replace(text, "$\'");
console.log(text);

Instead of printing "$'" as expected, this code outputs an empty string. This peculiar behavior can be attributed to the special meaning of the dollar sign in JavaScript regular expressions.

The dollar sign ($) in regular expressions denotes the end of the string. When used within string.replace, it instructs the method to replace the substring with the contents captured by the previous expression's capture group. In this case, there is no capture group, leading to an empty replacement string.

To resolve this issue and use the dollar sign as intended, the escape sequence $$ must be employed. This escape sequence informs JavaScript that the dollar sign should be treated as a literal character rather than a special symbol.

Here's the modified code:

text = text.replace(text, "$$'");

With this modification, the code will correctly print "$'" to the console, as the dollar sign is now treated as a character to be inserted into the replacement string.

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