Use the get parameter of the url in javascript

From my programming archive:

function querystring(key) {
   var re=new RegExp('(?:\\?|&)'+key+'=(.*?)(?=&|$)','gi');
   var r=[], m;
   while ((m=re.exec(document.location.search)) != null) r[r.length]=m[1];
   return r;
}

If the value doesn't exist, an empty array is returned.
If the value exists, an array is return that has one item, the value.
If several values with the name exists, an array containing each value is returned.

Examples:

var param1var = querystring("param1")[0];

document.write(querystring("name"));

if (querystring('id')=='42') alert('We apoligize for the inconvenience.');

if (querystring('button').length>0) alert(querystring('info'));

Here's how you could do it in Coffee Script (just if anyone is interested).

decodeURIComponent( v.split( "=" )[1] ) if decodeURIComponent( v.split( "=" )[0] ) == name for v in window.location.search.substring( 1 ).split( "&" )

Using jquery? I've used this before: http://projects.allmarkedup.com/jquery_url_parser/ and it worked pretty well.

This looked ok:

function gup( name ){
   name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
   var regexS = "[\\?&]"+name+"=([^&#]*)";
   var regex = new RegExp( regexS );
   var results = regex.exec( window.location.href );
   if( results == null )
      return "";
   else
      return results[1];
}

From http://www.netlobo.com/url_query_string_javascript.html

You can get the "search" part of the location object - and then parse it out.

var matches = /param1=([^&#=]*)/.exec(window.location.search);
var param1 = matches[1];

Here is a version that JSLint likes:

/*jslint browser: true */
var GET = {};
(function (input) {
    'use strict';
    if (input.length > 1) {
        var param = input.slice(1).replace(/\+/g, ' ').split('&'),
            plength = param.length,
            tmp,
            p;

        for (p = 0; p < plength; p += 1) {
            tmp = param[p].split('=');
            GET[decodeURIComponent(tmp[0])] = decodeURIComponent(tmp[1]);
        }
    }
}(window.location.search));

window.alert(JSON.stringify(GET));

Or if you need support for several values for one key like eg. ?key=value1&key=value2 you can use this:

/*jslint browser: true */
var GET = {};
(function (input) {
    'use strict';
    if (input.length > 1) {
        var params = input.slice(1).replace(/\+/g, ' ').split('&'),
            plength = params.length,
            tmp,
            key,
            val,
            obj,
            p;

        for (p = 0; p < plength; p += 1) {
            tmp = params[p].split('=');
            key = decodeURIComponent(tmp[0]);
            val = decodeURIComponent(tmp[1]);
            if (GET.hasOwnProperty(key)) {
                obj = GET[key];
                if (obj.constructor === Array) {
                    obj.push(val);
                } else {
                    GET[key] = [obj, val];
                }
            } else {
                GET[key] = val;
            }
        }
    }
}(window.location.search));

window.alert(JSON.stringify(GET));

I made this variation of gnarf's solution, so the call and the result is similar to PHP:

function S_GET(id){
    var a = new RegExp(id+"=([^&#=]*)");
    return decodeURIComponent(a.exec(window.location.search)[1]);
}

But as being called in a function slows the process, its better to use as global:

window['var_name'] = decodeURIComponent( /var_in_get=([^&#=]*)/.exec(window.location.search)[1] );