JavaScript - Regex: URL has a param

Question

I'm trying to create an analog for php's isset ($_GET[param]) but for JavaScript.
So long, I get this

[?&]param[&=]

But if param is at the end of URL (example.com?param) this regex won't work.
You can play with it here: https://regex101.com/r/fFeWPW/1

Answer 1

If you want to make sure your match ends with & , = or end of string, you may replace the [&=] character class with a (?:[&=]|$) alternation group that will match & , = or end of string (note that $ cannot be placed inside the character class as it would lose its special meaning there and will be treated as a $ symbol), or you may use a negative lookahead (?![^&=]) that fails the match if there is no & or = immediately after the current location, which might be a bit more efficient than an alternation group.

So, in your case, it will look like

[?&]param(?:[&=]|$)

or

[?&]param(?![^&=])

See a regex demo

JS demo:

 var strs = ['http://example.com?param', 'http://example.com?param=123', 'http://example.com?param&another','http://example.com?params']; var rx = /[?&]param(?![^&=])/; for (var s of strs) { console.log(s, "=>", rx.test(s)) }