How to retrieve GET parameters from JavaScript

Consider:

http://example.com/page.html?returnurl=%2Fadmin

For js within page.html, how can it retrieve GET parameters?

For the above simple example, func('returnurl') should be /admin.

But it should also work for complex query strings...

With the window.location object. This code gives you GET without the question mark.

window.location.search.substr(1)

From your example it will return returnurl=%2Fadmin

EDIT: I took the liberty of changing Qwerty's answer, which is really good, and as he pointed I followed exactly what the OP asked:

function findGetParameter(parameterName) {
    var result = null,
        tmp = [];
    location.search
        .substr(1)
        .split("&")
        .forEach(function (item) {
          tmp = item.split("=");
          if (tmp[0] === parameterName) result = decodeURIComponent(tmp[1]);
        });
    return result;
}

I removed the duplicated function execution from his code, replacing it a variable ( tmp ) and also I've added decodeURIComponent, exactly as OP asked. I'm not sure if this may or may not be a security issue.

Or otherwise with plain for loop, which will work even in IE8:

function findGetParameter(parameterName) {
    var result = null,
        tmp = [];
    var items = location.search.substr(1).split("&");
    for (var index = 0; index < items.length; index++) {
        tmp = items[index].split("=");
        if (tmp[0] === parameterName) result = decodeURIComponent(tmp[1]);
    }
    return result;
}

window.location.search will return everything from the ? on. This code below will remove the ?, use split to separate into key/value arrays, then assign named properties to the params object:

function getSearchParameters() {
    var prmstr = window.location.search.substr(1);
    return prmstr != null && prmstr != "" ? transformToAssocArray(prmstr) : {};
}

function transformToAssocArray( prmstr ) {
    var params = {};
    var prmarr = prmstr.split("&");
    for ( var i = 0; i < prmarr.length; i++) {
        var tmparr = prmarr[i].split("=");
        params[tmparr[0]] = tmparr[1];
    }
    return params;
}

var params = getSearchParameters();

You can then get the test parameter from http://myurl.com/?test=1 by calling params.test.

tl;dr solution on a single line of code using vanilla JavaScript

var queryDict = {}
location.search.substr(1).split("&").forEach(function(item) {queryDict[item.split("=")[0]] = item.split("=")[1]})

This is the simplest solution. It unfortunately does not handle multi-valued keys and encoded characters.

"?a=1&a=%2Fadmin&b=2&c=3&d&e"
> queryDict
a: "%2Fadmin"  // Overridden with the last value, not decoded.
b: "2"
c: "3"
d: undefined
e: undefined

Multi-valued keys and encoded characters?

See the original answer at How can I get query string values in JavaScript?.

"?a=1&b=2&c=3&d&e&a=5&a=t%20e%20x%20t&e=http%3A%2F%2Fw3schools.com%2Fmy%20test.asp%3Fname%3Dståle%26car%3Dsaab&a=%2Fadmin"
> queryDict
a: ["1", "5", "t e x t", "/admin"]
b: ["2"]
c: ["3"]
d: [undefined]
e: [undefined, "http://w3schools.com/my test.asp?name=ståle&car=saab"]

---

In your example, you would access the value like this:

"?returnurl=%2Fadmin"
> qd.returnurl    // ["/admin"]
> qd['returnurl'] // ["/admin"]
> qd.returnurl[0] // "/admin"

You should use URL and URLSearchParams native functions:

let url = new URL("https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8&q=mdn%20query%20string")
let params = new URLSearchParams(url.search);
let sourceid = params.get('sourceid') // 'chrome-instant'
let q = params.get('q') // 'mdn query string'
let ie = params.has('ie') // true
params.append('ping','pong')

console.log(sourceid)
console.log(q)
console.log(ie)
console.log(params.toString())
console.log(params.get("ping"))

https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams https://polyfill.io/v2/docs/features/

A more fancy way to do it: :)

var options = window.location.search.slice(1)
                      .split('&')
                      .reduce(function _reduce (/*Object*/ a, /*String*/ b) {
                        b = b.split('=');
                        a[b[0]] = decodeURIComponent(b[1]);
                        return a;
                      }, {});

This one uses a regular expression and returns null if the parameter doesn't exist or doesn't have any value:

function getQuery(q) {
   return (window.location.search.match(new RegExp('[?&]' + q + '=([^&]+)')) || [, null])[1];
}

I do it like this (to retrieve a specific get-parameter, here 'parameterName'):

var parameterValue = decodeURIComponent(window.location.search.match(/(\?|&)parameterName\=([^&]*)/)[2]);

Here I've made this code to transform the GET parameters into an object to use them more easily.

// Get Nav URL
function getNavUrl() {
    // Get URL
    return window.location.search.replace("?", "");
};

function getParameters(url) {
    // Params obj
    var params = {};
    // To lowercase
    url = url.toLowerCase();
    // To array
    url = url.split('&');

    // Iterate over URL parameters array
    var length = url.length;
    for(var i=0; i<length; i++) {
        // Create prop
        var prop = url[i].slice(0, url[i].search('='));
        // Create Val
        var value = url[i].slice(url[i].search('=')).replace('=', '');
        // Params New Attr
        params[prop] = value;
    }
    return params;
};

// Call of getParameters
console.log(getParameters(getNavUrl()));

var getQueryParam = function(param) {
    var found;
    window.location.search.substr(1).split("&").forEach(function(item) {
        if (param ==  item.split("=")[0]) {
            found = item.split("=")[1];
        }
    });
    return found;
};

I have created a simple JavaScript function to access GET parameters from URL.

Just include this JavaScript source and you can access get parameters. E.g.: in http://example.com/index.php?language=french, the language variable can be accessed as $_GET["language"]. Similarly, a list of all parameters will be stored in a variable $_GET_Params as an array. Both the JavaScript and HTML are provided in the following code snippet:

<!DOCTYPE html>
<html>
  <body>
    <!-- This script is required -->
    <script>
    function $_GET() {
      // Get the Full href of the page e.g. http://www.google.com/files/script.php?v=1.8.7&country=india
      var href = window.location.href;

      // Get the protocol e.g. http
      var protocol = window.location.protocol + "//";

      // Get the host name e.g. www.google.com
      var hostname = window.location.hostname;

      // Get the pathname e.g. /files/script.php
      var pathname = window.location.pathname;

      // Remove protocol part
      var queries = href.replace(protocol, '');

      // Remove host part
      queries = queries.replace(hostname, '');

      // Remove pathname part
      queries = queries.replace(pathname, '');

      // Presently, what is left in the variable queries is : ?v=1.8.7&country=india

      // Perform query functions if present
      if (queries != "" && queries != "?") {

    // Remove question mark '?'
        queries = queries.slice(1);

        // Split all the different queries
        queries = queries.split("&");

        // Get the number of queries
        var length = queries.length;

        // Declare global variables to store keys and elements
        $_GET_Params = new Array();
        $_GET = {};

        // Perform functions per query
        for (var i  = 0; i < length; i++) {

          // Get the present query
          var key = queries[i];

          // Split the query and the value
          key = key.split("=");

          // Assign value to the $_GET variable
          $_GET[key[0]] = [key[1]];

          // Assign value to the $_GET_Params variable
          $_GET_Params[i] = key[0];
        }
      }
    }

    // Execute the function
    $_GET();
    </script>
    <h1>GET Parameters</h1>
    <h2>Try to insert some get parameter and access it through JavaScript</h2>
  </body>
</html>

Here is another example based on Kat's and Bakudan's examples, but making it a just a bit more generic.

function getParams ()
{
    var result = {};
    var tmp = [];

    location.search
        .substr (1)
        .split ("&")
        .forEach (function (item)
        {
            tmp = item.split ("=");
            result [tmp[0]] = decodeURIComponent (tmp[1]);
        });

    return result;
}

location.getParams = getParams;

console.log (location.getParams());
console.log (location.getParams()["returnurl"]);

If you don't mind using a library instead of rolling your own implementation, check out https://github.com/jgallen23/querystring.

This solution handles URL decoding:

var params = function() {
    function urldecode(str) {
        return decodeURIComponent((str+'').replace(/\+/g, '%20'));
    }

    function transformToAssocArray( prmstr ) {
        var params = {};
        var prmarr = prmstr.split("&");
        for ( var i = 0; i < prmarr.length; i++) {
            var tmparr = prmarr[i].split("=");
            params[tmparr[0]] = urldecode(tmparr[1]);
        }
        return params;
    }

    var prmstr = window.location.search.substr(1);
    return prmstr != null && prmstr != "" ? transformToAssocArray(prmstr) : {};
}();

Usage:

console.log('someParam GET value is', params['someParam']);

My solution expands on @tak3r's.

It returns an empty object when there are no query parameters and supports the array notation ?a=1&a=2&a=3:

function getQueryParams () {
  function identity (e) { return e; }
  function toKeyValue (params, param) {
    var keyValue = param.split('=');
    var key = keyValue[0], value = keyValue[1];

    params[key] = params[key]?[value].concat(params[key]):value;
    return params;
  }
  return decodeURIComponent(window.location.search).
    replace(/^\?/, '').split('&').
    filter(identity).
    reduce(toKeyValue, {});
}

To get the parameters as a JSON object:

alert(getUrlParameters().toSource())

function explode(delim, str)
{
    return str.split(delim);
}

function getUrlParameters()
{
    var out = {};
    var str = window.location.search.replace("?", "");
    var subs = explode('&', str);
    for(var i = 0; i < subs.length; ++i)
    {
        var vals = explode('=', subs[i]);
        out[vals[0]] = vals[1];
    }
    return out;
}

You can use the search function available in the location object. The search function gives the parameter part of the URL. Details can be found in Location Object.

You will have to parse the resulting string for getting the variables and their values, e.g. splitting them on '='.

If you are using AngularJS, you can use $routeParams using ngRoute module

You have to add a module to your app

angular.module('myApp', ['ngRoute'])

Now you can use service $routeParams:

.controller('AppCtrl', function($routeParams) {
  console.log($routeParams); // JSON object
}