How to search replace with regex and keep case as original in javascript

Question

Here is my problem. I have a string with mixed case in it. I want to search regardless of case and then replace the matches with some characters either side of the matches.

Answer 1

This can be done using a back-reference:

var s2 = s.replace(/your complex regex/g, "#$&#");

The back-reference $& brings in the entire match. If you want to match "abc" in any case:

var s2 = s.replace(/abc/ig, "#$&#");

If you only want to bring in part of a larger pattern, you can refer to it by its group number:

var s2 = s.replace(/some (part) of a string/ig, "#$1#");

Groups are numbered by their opening parenthesis, from left to right, from $1 to $9.