Question

I want to use a string to perform a global regex, but it might have regex characters in it. What’s the best way to escape all regex characters in a string before building a regex with it?

Basically I might have something like this;

var test = 'test.';
var regex = new RegExp(test, 'ig');

I need ‘test.’ to become ‘test\.’ so it doesn’t behave in unexpected ways.

Answer 1

new RegExp(test.replace(/[#-.]|[[-^]|[?|{}]/g, '\\$&'));

This escapes the following:

• The characters between # and ., so: #$%&'()*+,-.
• The four characters [, \, ], and ^
• These characters ?, |, {, }

…by prepending a backslash before each occurrence (as $& Inserts the matched substring, and the g flag means to replace all instances.)

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Alternatively, if you’re looking for a shorter version, try:

new RegExp(test.replace(/[#-}]/g, '\\$&'));

This will end up escaping a lot more than it should, but it won’t harm anything.