Update: June-2021

For a specific case when you need all query params:

const urlSearchParams = new URLSearchParams(window.location.search);const params = Object.fromEntries(urlSearchParams.entries());

Update: Sep-2018

You can use URLSearchParams which is simple and has decent (but not complete) browser support.

const urlParams = new URLSearchParams(window.location.search);const myParam = urlParams.get('myParam');

Original

You don't need jQuery for that purpose. You can use just some pure JavaScript:

function getParameterByName(name, url = window.location.href) {    name = name.replace(/[\[\]]/g, '\\$&');    var regex = new RegExp('[?&]' + name + '(=([^&#]*)|&|#|$)'),        results = regex.exec(url);    if (!results) return null;    if (!results[2]) return '';    return decodeURIComponent(results[2].replace(/\+/g, ' '));}

Usage:

// query string: ?foo=lorem&bar=&bazvar foo = getParameterByName('foo'); // "lorem"var bar = getParameterByName('bar'); // "" (present with empty value)var baz = getParameterByName('baz'); // "" (present with no value)var qux = getParameterByName('qux'); // null (absent)

NOTE: If a parameter is present several times (?foo=lorem&foo=ipsum), you will get the first value (lorem). There is no standard about this and usages vary, see for example this question: Authoritative position of duplicate HTTP GET query keys.

NOTE: The function is case-sensitive. If you prefer case-insensitive parameter name, add 'i' modifier to RegExp

NOTE: If you're getting a no-useless-escape eslint error, you can replace name = name.replace(/[\[\]]/g, '\\$&'); with name = name.replace(/[[\]]/g, '\\$&').

This is an update based on the new URLSearchParams specs to achieve the same result more succinctly. See answer titled "URLSearchParams" below.

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!

UPDATED

A new capability would be to retrieve repeated params as following myparam=1&myparam=2. There is not a specification, however, most of the current approaches follow the generation of an array.

myparam = ["1", "2"]

So, this is the approach to manage it:

let urlParams = {};(window.onpopstate = function () {    let 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);    while (match = search.exec(query)) {        if (decode(match[1]) in urlParams) {            if (!Array.isArray(urlParams[decode(match[1])])) {                urlParams[decode(match[1])] = [urlParams[decode(match[1])]];            }            urlParams[decode(match[1])].push(decode(match[2]));        } else {            urlParams[decode(match[1])] = decode(match[2]);        }    }})();

ES2015 (ES6)

getQueryStringParams = query => {    return query        ? (/^[?#]/.test(query) ? query.slice(1) : query)            .split('&')            .reduce((params, param) => {                    let [key, value] = param.split('=');                    params[key] = value ? decodeURIComponent(value.replace(/\+/g, ' ')) : '';                    return params;                }, {}            )        : {}};

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"];    // 123qs["name"];     // query stringqs["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. It does not work because some variables are undefined.

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 then they store the value of d, otherwise they 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(paramsArray) {        let params = {};        for (let i = 0; i < paramsArray.length; ++i)        {            let param = paramsArray[i]                .split('=', 2);                        if (param.length !== 2)                continue;                        params[param[0]] = decodeURIComponent(param[1].replace(/\+/g, " "));        }                    return params;    })(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 objecthistory.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