If you're using jQuery, you can use a library, such as jQuery BBQ: Back Button & Query Library.

...jQuery BBQ provides a full .deparam() method, along with both hash state management, and fragment / query string parse and merge utility methods.

Edit: Adding Deparam Example:

 var DeparamExample = function() {
            var params = $.deparam.querystring();

            //nameofparam is the name of a param from url
            //code below will get param if ajax refresh with hash
            if (typeof params.nameofparam == 'undefined') {
                params = jQuery.deparam.fragment(window.location.href);
            }
            
            if (typeof params.nameofparam != 'undefined') {
                var paramValue = params.nameofparam.toString();
                  
            }
        };

If you want to just use plain JavaScript, you could use...

var getParamValue = (function() {
    var params;
    var resetParams = function() {
            var query = window.location.search;
            var regex = /[?&;](.+?)=([^&;]+)/g;
            var match;

            params = {};

            if (query) {
                while (match = regex.exec(query)) {
                    params[match[1]] = decodeURIComponent(match[2]);
                }
            }    
        };

    window.addEventListener
    && window.addEventListener('popstate', resetParams);

    resetParams();

    return function(param) {
        return params.hasOwnProperty(param) ? params[param] : null;
    }

})();​

Because of the new HTML History API and specifically history.pushState() and history.replaceState(), the URL can change which will invalidate the cache of parameters and their values.

This version will update its internal cache of parameters each time the history changes.

Roshambo on snipplr.com has a simple script to achieve this described in Get URL Parameters with jQuery | Improved. With his script you also easily get to pull out just the parameters you want.

Here's the gist:

$.urlParam = function(name, url) {
    if (!url) {
     url = window.location.href;
    }
    var results = new RegExp('[\\?&]' + name + '=([^&#]*)').exec(url);
    if (!results) { 
        return undefined;
    }
    return results[1] || undefined;
}

Then just get your parameters from the query string.

So if the URL/query string was xyz.com/index.html?lang=de.

Just call var langval = $.urlParam('lang');, and you've got it.

UZBEKJON has a great blog post on this as well, Get URL parameters & values with jQuery.

Some of the solutions posted here are inefficient. Repeating the regular expression search every time the script needs to access a parameter is completely unnecessary, one single function to split up the parameters into an associative-array style object is enough. If you're not working with the HTML 5 History API, this is only necessary once per page load. The other suggestions here also fail to decode the URL correctly.

var urlParams;
(window.onpopstate = function () {
    var match,
        pl     = /\+/g,  // Regex for replacing addition symbol with a space
        search = /([^&=]+)=?([^&]*)/g,
        decode = function (s) { return decodeURIComponent(s.replace(pl, " ")); },
        query  = window.location.search.substring(1);

    urlParams = {};
    while (match = search.exec(query))
       urlParams[decode(match[1])] = decode(match[2]);
})();

Example querystring:

?i=main&mode=front&sid=de8d49b78a85a322c4155015fdce22c4&enc=+Hello%20&empty

Result:

 urlParams = {
    enc: " Hello ",
    i: "main",
    mode: "front",
    sid: "de8d49b78a85a322c4155015fdce22c4",
    empty: ""
}

alert(urlParams["mode"]);
// -> "front"

alert("empty" in urlParams);
// -> true

This could easily be improved upon to handle array-style query strings too. An example of this is here, but since array-style parameters aren't defined in RFC 3986 I won't pollute this answer with the source code. For those interested in a "polluted" version, look at campbeln's answer below.

Also, as pointed out in the comments, ; is a legal delimiter for key=value pairs. It would require a more complicated regex to handle ; or &, which I think is unnecessary because it's rare that ; is used and I would say even more unlikely that both would be used. If you need to support ; instead of &, just swap them in the regex.

<script>var urlParams = <?php echo json_encode($_GET, JSON_HEX_TAG);?>;</script>

Much simpler!

function GET() {
        var data = [];
        for(x = 0; x < arguments.length; ++x)
            data.push(location.href.match(new RegExp("/\?".concat(arguments[x],"=","([^\n&]*)")))[1])
                return data;
    }


example:
data = GET("id","name","foo");
query string : ?id=3&name=jet&foo=b
returns:
    data[0] // 3
    data[1] // jet
    data[2] // b
or
    alert(GET("id")[0]) // return 3

Without jQuery

var qs = (function(a) {
    if (a == "") return {};
    var b = {};
    for (var i = 0; i < a.length; ++i)
    {
        var p=a[i].split('=', 2);
        if (p.length == 1)
            b[p[0]] = "";
        else
            b[p[0]] = decodeURIComponent(p[1].replace(/\+/g, " "));
    }
    return b;
})(window.location.search.substr(1).split('&'));

With an URL like ?topic=123&name=query+string, the following will return:

qs["topic"];    // 123
qs["name"];     // query string
qs["nothere"];  // undefined (object)

Google method

Tearing Google's code I found the method they use: getUrlParameters

function (b) {
    var c = typeof b === "undefined";
    if (a !== h && c) return a;
    for (var d = {}, b = b || k[B][vb], e = b[p]("?"), f = b[p]("#"), b = (f === -1 ? b[Ya](e + 1) : [b[Ya](e + 1, f - e - 1), "&", b[Ya](f + 1)][K](""))[z]("&"), e = i.dd ? ia : unescape, f = 0, g = b[w]; f < g; ++f) {
        var l = b[f][p]("=");
        if (l !== -1) {
            var q = b[f][I](0, l),
                l = b[f][I](l + 1),
                l = l[Ca](/\+/g, " ");
            try {
                d[q] = e(l)
            } catch (A) {}
        }
    }
    c && (a = d);
    return d
}

It is obfuscated, but it is understandable.

They start to look for parameters on the url from ? and also from the hash #. Then for each parameter they split in the equal sign b[f][p]("=") (which looks like indexOf, they use the position of the char to get the key/value). Having it split they check whether the parameter has a value or not, if it has they store the value of d, if not it just continue.

In the end the object d is returned, handling escaping and the + sign. This object is just like mine, it has the same behavior.

My method as a jQuery plugin

(function($) {
    $.QueryString = (function(a) {
        if (a == "") return {};
        var b = {};
        for (var i = 0; i < a.length; ++i)
        {
            var p=a[i].split('=', 2);
            if (p.length != 2) continue;
            b[p[0]] = decodeURIComponent(p[1].replace(/\+/g, " "));
        }
        return b;
    })(window.location.search.substr(1).split('&'))
})(jQuery);

Usage

//Get a param
$.QueryString.param
//-or-
$.QueryString["param"]
//This outputs something like...
//"val"

//Get all params as object
$.QueryString
//This outputs something like...
//Object { param: "val", param2: "val" }

//Set a param (only in the $.QueryString object, doesn't affect the browser's querystring)
$.QueryString.param = "newvalue"
//This doesn't output anything, it just updates the $.QueryString object

//Convert object into string suitable for url a querystring (Requires jQuery)
$.param($.QueryString)
//This outputs something like...
//"param=newvalue&param2=val"

//Update the url/querystring in the browser's location bar with the $.QueryString object
history.replaceState({}, '', "?" + $.param($.QueryString));
//-or-
history.pushState({}, '', "?" + $.param($.QueryString));

Performance test (split method against regex method) (jsPerf)

Preparation code: methods declaration

Split test code

var qs = window.GetQueryString(query);

var search = qs["q"];
var value = qs["value"];
var undef = qs["undefinedstring"];

Regex test code

var search = window.getParameterByName("q");
var value = window.getParameterByName("value");
var undef = window.getParameterByName("undefinedstring");

Testing in Firefox 4.0 x86 on Windows Server 2008 R2 / 7 x64

• Split method: 144,780 ±2.17% fastest
• Regex method: 13,891 ±0.85% | 90% slower

Here's my stab at making Andy E's excellent solution into a full fledged jQuery plugin:

;(function ($) {
    $.extend({      
        getQueryString: function (name) {           
            function parseParams() {
                var params = {},
                    e,
                    a = /\+/g,  // Regex for replacing addition symbol with a space
                    r = /([^&=]+)=?([^&]*)/g,
                    d = function (s) { return decodeURIComponent(s.replace(a, " ")); },
                    q = window.location.search.substring(1);

                while (e = r.exec(q))
                    params[d(e[1])] = d(e[2]);

                return params;
            }

            if (!this.queryStringParams)
                this.queryStringParams = parseParams(); 

            return this.queryStringParams[name];
        }
    });
})(jQuery);

The syntax is:

var someVar = $.getQueryString('myParam');

Best of both worlds!

Here is my version of query string parsing code on GitHub.

It's "prefixed" with jquery.*, but the parsing function itself don't use jQuery. It's pretty fast, but still open for few simple performance optimizations.

Also it supports list & hash-tables encoding in the URL, like:

arr[]=10&arr[]=20&arr[]=100

or

hash[key1]=hello&hash[key2]=moto&a=How%20are%20you

jQuery.toQueryParams = function(str, separator) {
    separator = separator || '&'
    var obj = {}
    if (str.length == 0)
        return obj
    var c = str.substr(0,1)
    var s = c=='?' || c=='#'  ? str.substr(1) : str; 

    var a = s.split(separator)
    for (var i=0; i<a.length; i++) {
        var p = a[i].indexOf('=')
        if (p < 0) {
            obj[a[i]] = ''
            continue
        }
        var k = decodeURIComponent(a[i].substr(0,p)),
            v = decodeURIComponent(a[i].substr(p+1))

        var bps = k.indexOf('[')
        if (bps < 0) {
            obj[k] = v
            continue;
        } 

        var bpe = k.substr(bps+1).indexOf(']')
        if (bpe < 0) {
            obj[k] = v
            continue;
        }

        var bpv = k.substr(bps+1, bps+bpe-1)
        var k = k.substr(0,bps)
        if (bpv.length <= 0) {
            if (typeof(obj[k]) != 'object') obj[k] = []
            obj[k].push(v)
        } else {
            if (typeof(obj[k]) != 'object') obj[k] = {}
            obj[k][bpv] = v
        }
    }
    return obj;

}

Code golf:

var a = location.search&&location.search.substr(1).replace(/\+/gi," ").split("&");
for (var i in a) {
    var s = a[i].split("=");
    a[i]  = a[unescape(s[0])] = unescape(s[1]);
}

Display it!

for (i in a) {
    document.write(i + ":" + a[i] + "<br/>");   
};

On my Mac: test.htm?i=can&has=cheezburger displays

0:can
1:cheezburger
i:can
has:cheezburger

Roshambo jQuery method wasn't taking care of decode URL

http://snipplr.com/view/26662/get-url-parameters-with-jquery--improved/

Just added that capability also while adding in the return statement

return decodeURIComponent(results[1].replace(/\+/g, " ")) || 0;

Now you can find the updated gist:

$.urlParam = function(name){
var results = new RegExp('[\\?&]' + name + '=([^&#]*)').exec(window.location.href);
if (!results) { return 0; }
return decodeURIComponent(results[1].replace(/\+/g, " ")) || 0;
}

This is a function I created a while back and I'm quite happy with. It is not case sensitive - which is handy. Also, if the requested QS doesn't exist, it just returns an empty string.

I use a compressed version of this. I'm posting uncompressed for the novice types to better explain what's going on.

I'm sure this could be optimized or done differently to work faster, but it's always worked great for what I need.

Enjoy.

function getQSP(sName, sURL) {
    var theItmToRtn = "";
    var theSrchStrg = location.search;
    if (sURL) theSrchStrg = sURL;
    var sOrig = theSrchStrg;
    theSrchStrg = theSrchStrg.toUpperCase();
    sName = sName.toUpperCase();
    theSrchStrg = theSrchStrg.replace("?", "&") theSrchStrg = theSrchStrg + "&";
    var theSrchToken = "&" + sName + "=";
    if (theSrchStrg.indexOf(theSrchToken) != -1) {
        var theSrchTokenLth = theSrchToken.length;
        var theSrchTokenLocStart = theSrchStrg.indexOf(theSrchToken) + theSrchTokenLth;
        var theLocOfNextAndSign = theSrchStrg.indexOf("&", theSrchTokenLocStart);
        theItmToRtn = unescape(sOrig.substring(theSrchTokenLocStart, theLocOfNextAndSign));
    }
    return unescape(theItmToRtn);
}

Improved version of Artem Barger's answer:

function getParameterByName(name) {
    var match = RegExp('[?&]' + name + '=([^&]*)').exec(window.location.search);
    return match && decodeURIComponent(match[1].replace(/\+/g, ' '));
}

For more information on improvement see: http://james.padolsey.com/javascript/bujs-1-getparameterbyname/

I use regular expressions a lot, but not for that.

It seems easier and more efficient to me to read the query string once in my application, and build an object from all the key/value pairs like:

var search = function() {
  var s = window.location.search.substr(1),
    p = s.split(/\&/), l = p.length, kv, r = {};
  if (l === 0) {return false;}
  while (l--) {
    kv = p[l].split(/\=/);
    r[kv[0]] = decodeURIComponent(kv[1] || '') || true;
  }
  return r;
}();

For a URL like http://domain.com?param1=val1&param2=val2 you can get their value later in your code as search.param1 and search.param2.

Just another recommendation. The plugin Purl allows to retrieve all parts of URL, including anchor, host, etc.

It can be used with or without jQuery.

Usage is very simple and cool:

var url = $.url('http://allmarkedup.com/folder/dir/index.html?item=value'); // jQuery version
var url = purl('http://allmarkedup.com/folder/dir/index.html?item=value'); // plain JS version
url.attr('protocol'); // returns 'http'
url.attr('path'); // returns '/folder/dir/index.html'

However, as of Nov 11, 2014, Purl is no longer maintained and the author recommends using URI.js instead. The jQuery plugin is different in that it focuses on elements - for usage with strings, just use URI directly, with or without jQuery. Similar code would look as such, fuller docs here:

var url = new URI('http://allmarkedup.com/folder/dir/index.html?item=value'); // plain JS version
url.protocol(); // returns 'http'
url.path(); // returns '/folder/dir/index.html'

I would rather use split() instead of Regex for this operation:

function getUrlParams() {
    var result = {};
    var params = (window.location.search.split('?')[1] || '').split('&');
    for(var param in params) {
        if (params.hasOwnProperty(param)) {
            paramParts = params[param].split('=');
            result[paramParts[0]] = decodeURIComponent(paramParts[1] || "");
        }
    }
    return result;
}

I took this answer and added support for optionally passing the URL in as a parameter; falls back to window.location.search. Obviously this is useful for getting the query string parameters from URLs that are not the current page:

(function($, undef) {
  $.QueryString = function(url) {
    var pairs, qs = null, index, map = {};
    if(url == undef){
      qs = window.location.search.substr(1);
    }else{
      index = url.indexOf('?');
      if(index == -1) return {};
      qs = url.substring(index+1);
    }
    pairs = qs.split('&');
    if (pairs == "") return {};
    for (var i = 0; i < pairs.length; ++i)
    {
      var p = pairs[i].split('=');
      if(p.length != 2) continue;
      map[p[0]] = decodeURIComponent(p[1].replace(/\+/g, " "));
    }
    return map;
  };
})(jQuery);

Here's my edit to this excellent answer - with added ability to parse query strings with keys without values.

var url = 'http://sb.com/reg/step1?param';
var qs = (function(a) {
    if (a == "") return {};
    var b = {};
    for (var i = 0; i < a.length; ++i) {
        var p=a[i].split('=', 2);
        if (p[1]) p[1] = decodeURIComponent(p[1].replace(/\+/g, " "));
        b[p[0]] = p[1];
    }
    return b;
})((url.split('?'))[1].split('&'));

IMPORTANT! The parameter for that function in the last line is different. It's just an example of how one can pass an arbitrary URL to it. You can use last line from Bruno's answer to parse the current URL.

So what exactly changed? With url http://sb.com/reg/step1?param= results will be same. But with url http://sb.com/reg/step1?param Bruno's solution returns an object without keys, while mine returns an object with key param and undefined value.

The following code will create an object which has two methods:

1. isKeyExist: Check if a particular parameter exist
2. getValue: Get the value of a particular parameter.

var QSParam = new function() {
       var qsParm = {};
       var query = window.location.search.substring(1);
       var params = query.split('&');
       for (var i = 0; i < params.length; i++) {
           var pos = params[i].indexOf('=');
           if (pos > 0) {
               var key = params[i].substring(0, pos);
               var val = params[i].substring(pos + 1);
               qsParm[key] = val;
           }
       }
       this.isKeyExist = function(query){
           if(qsParm[query]){
               return true;
           }
           else{
              return false;
           }
       };
       this.getValue = function(query){
           if(qsParm[query])
           {
               return qsParm[query];
           }
           throw "URL does not contain query "+ query;
       }
};

Try this:

String.prototype.getValueByKey = function(k){
    var p = new RegExp('\\b'+k+'\\b','gi');
    return this.search(p) != -1 ? decodeURIComponent(this.substr(this.search(p)+k.length+1).substr(0,this.substr(this.search(p)+k.length+1).search(/(&|;|$)/))) : "";
};

Then call it like so:

if(location.search != "") location.search.getValueByKey("id");

You can use this for cookies also:

if(navigator.cookieEnabled) document.cookie.getValueByKey("username");

This only works for strings that have key=value[&|;|$]... will not work on objects/arrays.

If you don't want to use String.prototype... move it to a function and pass the string as an argument

I like Ryan Phelan's solution. But I don't see any point of extending jQuery for that? There is no usage of jQuery functionality.

On other hand I like the built-in function in Google Chrome: window.location.getParameter.

So why not to use this? Okay, other browsers don't have. So let's create this function if it does not exist:

if (!window.location.getParameter ) {
  window.location.getParameter = function(key) {
    function parseParams() {
        var params = {},
            e,
            a = /\+/g,  // Regex for replacing addition symbol with a space
            r = /([^&=]+)=?([^&]*)/g,
            d = function (s) { return decodeURIComponent(s.replace(a, " ")); },
            q = window.location.search.substring(1);

        while (e = r.exec(q))
            params[d(e[1])] = d(e[2]);

        return params;
    }

    if (!this.queryStringParams)
        this.queryStringParams = parseParams(); 

    return this.queryStringParams[key];
  };
}

This function is more or less from Ryan Phelan, but it is wrapped differently: clear name and no dependencies of other javascript libraries. More about this function on my blog.

function getUrlVar(key){
    var result = new RegExp(key + "=([^&]*)", "i").exec(window.location.search); 
    return result && unescape(result[1]) || ""; 
}

https://gist.github.com/1771618

Keep it simple in plain JavaScript code:

function qs(key) {
    var vars = [], hash;
    var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
    for(var i = 0; i < hashes.length; i++)
    {
        hash = hashes[i].split('=');
        vars.push(hash[0]);
        vars[hash[0]] = hash[1];
    }
    return vars[key];
}

Call it from anywhere in the JavaScript code:

var result = qs('someKey');

If you're doing more URL manipulation than simply parsing the querystring, you may find URI.js helpful. It is a library for manipulating URLs - and comes with all the bells and whistles. (Sorry for self-advertising here)

to convert your querystring into a map:

var data = URI('?foo=bar&bar=baz&foo=world').query(true);
data == {
  "foo": ["bar", "world"],
  "bar": "baz"
}

(URI.js also "fixes" bad querystrings like ?&foo&&bar=baz& to ?foo&bar=baz)

Here's my own take on this. This first function decodes a URL string into an object of name/value pairs:

url_args_decode = function (url) {
  var args_enc, el, i, nameval, ret;
  ret = {};
  // use the DOM to parse the URL via an 'a' element
  el = document.createElement("a");
  el.href = url;
  // strip off initial ? on search and split
  args_enc = el.search.substring(1).split('&');
  for (i = 0; i < args_enc.length; i++) {
    // convert + into space, split on =, and then decode 
    args_enc[i].replace(/\+/g, ' ');
    nameval = args_enc[i].split('=', 2);
    ret[decodeURIComponent(nameval[0])]=decodeURIComponent(nameval[1]);
  }
  return ret;
};

And as an added bonus, if you change some of the args, you can use this second function to put the array of args back into the URL string:

url_args_replace = function (url, args) {
  var args_enc, el, name;
  // use the DOM to parse the URL via an 'a' element
  el = document.createElement("a");
  el.href = url;
  args_enc = [];
  // encode args to go into url
  for (name in args) {
    if (args.hasOwnProperty(name)) {
      name = encodeURIComponent(name);
      args[name] = encodeURIComponent(args[name]);
      args_enc.push(name + '=' + args[name]);
    }
  }
  if (args_enc.length > 0) {
    el.search = '?' + args_enc.join('&');
  } else {
    el.search = '';
  }
  return el.href;
};

http://someurl.com?key=value&keynovalue&keyemptyvalue=&&keynovalue=nowhasvalue#somehash

• Regular key/value pair (?param=value)
• Keys w/o value (?param : no equal sign or value)
• Keys w/ empty value (?param= : equal sign, but no value to right of equal sign)
• Repeated Keys (?param=1&param=2)
• Removes Empty Keys (?&& : no key or value)

Code:

• var queryString = window.location.search || '';
  var keyValPairs = [];
  var params      = {};
  queryString     = queryString.substr(1);
  
  if (queryString.length)
  {
     keyValPairs = queryString.split('&');
     for (pairNum in keyValPairs)
     {
        var key = keyValPairs[pairNum].split('=')[0];
        if (!key.length) continue;
        if (typeof params[key] === 'undefined')
           params[key] = [];
        params[key].push(keyValPairs[pairNum].split('=')[1]);
     }
  }
  

How to Call:

• params['key'];  // returns an array of values (1..n)
  

Output:

• key            ["value"]
  keyemptyvalue  [""]
  keynovalue     [undefined, "nowhasvalue"]
  

This one works fine

function getQuerystring(key) {
    var query = window.location.search.substring(1);
    alert(query);
    var vars = query.split("&");
    for (var i = 0; i < vars.length; i++) {
        var pair = vars[i].split("=");
        if (pair[0] == key) {
            return pair[1];
        }
    }
}

taken from here

The following function returns an object version of your queryString. You can simply write obj.key1 and obj.key2 to access values of key1 and key2 in parameter.

function getQueryStringObject()
{
    var querystring = document.location.search.replace('?','').split( '&' );
    var objQueryString={};
    var key="",val="";
    if(typeof querystring == 'undefined')
    {
        return (typeof querystring);
    }
    for(i=0;i<querystring.length;i++)
    {
        key=querystring[i].split("=")[0];
        val=querystring[i].split("=")[1];
        objQueryString[key] = val;
    }
    return objQueryString;
}

And to use this function you can write

var obj= getQueryStringObject();
alert(obj.key1);

I like this one (taken from jquery-howto.blogspot.co.uk):

// get an array with all querystring values
// example: var valor = getUrlVars()["valor"];
function getUrlVars() {
    var vars = [], hash;
    var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
    for (var i = 0; i < hashes.length; i++) {
        hash = hashes[i].split('=');
        vars.push(hash[0]);
        vars[hash[0]] = hash[1];
    }
    return vars;
}

Works great for me.

URLSearchParams

Firefox 44+, Opera 36+ and Chrome 49+ support the URLSearchParams API:

• Chrome Announcement and details
• Opera Announcement and details
• Firefox Announcement and details

It is not standardized by W3C, but it is a living standard by WhatWG.

You can use it on location, but you need to remove the ? question mark (for example, with .slice(1)):

let params = new URLSearchParams(location.search.slice(1));

Or of course on any URL:

let url = new URL('https://example.com?foo=1&bar=2');
let params = new URLSearchParams(url.search.slice(1));

And you read/set parameters through the get(KEY), set(KEY, VALUE), append(KEY, VALUE) api. You can also iterate over all values for (let p of params) {}.

There's also a google-suggested URLSearchParams polyfill and a sample page if you want to start using this API without relying on latest version of Chrome/Firefox/Opera.

Here is a fast way to get an object similar to the PHP $_GET array:

function get_query(){
    var url = location.search;
    var qs = url.substring(url.indexOf('?') + 1).split('&');
    for(var i = 0, result = {}; i < qs.length; i++){
        qs[i] = qs[i].split('=');
        result[qs[i][0]] = decodeURIComponent(qs[i][1]);
    }
    return result;
}

Usage:

var $_GET = get_query();

For the query string x=5&y&z=hello&x=6 this returns the object:

{
  x: "6",
  y: undefined,
  z: "hello"
}