Can someone tell me the purpose of the second capture group in the jQuery rts regular expression?

Question

In Jeff Roberson's jQuery Regular Expressions Review he proposes changing the rts regular expression in jQuery's ajax.js from /(\?|&)_=.*?(&|$)/ to /([?&])_=[^&\r\n]*(&?)/. In both versions, what is the purpose of the second capture group? The code does a replacement of the current random timestamp with a new random timestamp:

var ts = jQuery.now();
// try replacing _= if it is there
var ret = s.url.replace(rts, "$1_=" + ts + "$2");

Doesn't it only replace what it matches? I am thinking this does the same:

var ret = s.url.replace(/([?&])_=[^&\r\n]*/, "$1_=" + ts);

Can someone explain the purpose of the second capture group?

Answer 1

I think you're right. It was needed in the original because matching the ampersand or end-of-string was how the .*? knew when to stop. In Jeff's version that's no longer necessary.

Answer 2

As the author of the article I can't tell you the reason for the second capture group. My intent with the article was to take existing regexes and simply make them more efficient - i.e. they should all match the same text - just do it faster. Unfortunately I did not have time to delve deeply into the code to see exactly how each and every one of them was being used. I assumed that the capture group for this one was there for a reason so I did not mess with it.