Why Does `string.replace` Produce an Empty String When Replacing with a Dollar Sign ($)?

Weird String Replacement Behavior Using the Dollar Sign ($) in string.replace

When attempting to replace a string using the string.replace method and specifying the replacement as a dollar sign ($), an unexpected result of an empty string may arise. This phenomenon occurs due to the special significance of the dollar sign in JavaScript regular expressions and the string.replace method.

To accurately replace a string with a dollar sign, the replacement string should be specified as $$ instead of $. This is because the dollar sign, when used in regular expressions, has specific meanings related to backreferences, capture groups, and the end of the string.

For example, consider the following code:

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

In this case, the empty string is printed because the replacement string is interpreted as a reference to a capture group. Since there are no capture groups defined in the regular expression, the result is an empty string.

To correct this behavior, use $$ as the replacement string:

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

By using $$ instead of $, the dollar sign is treated as a literal character, and the intended replacement occurs. This is because $$ escapes the special meaning of the dollar sign in regular expressions.

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