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When a URL contains the GET params the keyed values can be extracted from the location.href or location.search

Here is a very concise example care of Jumper (efnet):

(function(){
   for(var Q=QueryString={},
           h=location.href,
           s=h.substring(h.indexOf("?")+1),
           qs=s.split("&"),
           i=0,k,v;
           k=qs[i++];
           v=k.split("="),
           Q[v[0]]=unescape(v[1]));
})()

The above example will create an object named QueryString which contains a key value pairs for each param in the Querystring.

Using the URL : http://www.google.com/search?num=100&hl=en&safe=off&q=javascript+querystring& each params can be reference :

num : QueryString.num or QueryString["num"]

100

hl : QueryString.hl or QueryString["hl"]

en

safe : QueryString.safe or QueryString["safe"]

off

q : QueryString.q or QueryString["q"]

javascript+querystring

Please Note : The example above has been laied out to make it legible and would be better expressed :

(function(){for(var Q=QueryString={},h=location.href,s=h.substring(h.indexOf("?")+1),qs=s.split("&"),i=0,k,v;k=qs[i++];v=k.split("="),Q[v[0]]=unescape(v[1]));})()

Another one

Here's another example function, that makk wrote, that will give you all key value pairs of an url querystring.

/* deserializeUrl: returns object literal containing
   all key value pairs of the url search part.
 */
function deserializeUrl() {
	var ret = {};
	var search = location.search.slice(1);
	if (search) {
		for (var pairs = search.split('&'), i = 0, l = pairs.length, pair; i < l; i++) {
			pair = pairs[i].split('=');
			key = decodeURIComponent(pair[0]);
			val = decodeURIComponent(pair[1]);
			if (key in ret) {
				if (!(ret[key] instanceof Array)) {
					ret[key] = [ret[key]];
				}
				ret[key].push(val);
			} else {
				ret[key] = val;
			}
		}
	}
	return ret;
}

/* Usage:
   given an url like: http://www.aoe.com/uid?foo=bar&id=1&serv=foo&serv=makk
   running `deserializeUrl' will rusult in the following:
   var obj = deserializeUrl();
   obj['foo'] which will contian 'bar'
   obj['serv'] which will contain an array ['foo', 'makk']
   obj['id'] which will contian '1'
   note that '1' is not a number but a string
 */