JavaScript query string

You can extract the key/value pairs from the location.search property, this property has the part of the URL that follows the ? symbol, including the ? symbol.

function queryObj() {
    var result = {}, queryString = location.search.slice(1),
        re = /([^&=]+)=([^&]*)/g, m;

    while (m = re.exec(queryString)) {
        result[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);
    }

    return result;
}

// Usage:
var myParam = queryObj()["myParam"];

Update:

No need to use regex:

function queryObj() {
    var result = {}, keyValuePairs = location.search.slice(1).split('&');

    keyValuePairs.forEach(function(keyValuePair) {
        keyValuePair = keyValuePair.split('=');
        result[keyValuePair[0]] = keyValuePair[1] || '';
    });

    return result;
}

For IE8- support include this tiny Array.forEach* polyfill:

if ( !Array.prototype.forEach ) {
    Array.prototype.forEach = function(fn, scope) {
        for(var i = 0, len = this.length; i < len; ++i) {
            fn.call(scope, this[i], i, this);
        }
    }
}

From: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/forEach

*Array.forEach aka the better for loop

If you have the querystring on hand, use this:

 /**
 * @param qry the querystring
 * @param name name of parameter
 * @returns the parameter specified by name
 * @author [email protected]
 */

function getQueryStringParameter(qry,name){
    if(typeof qry !== undefined && qry !== ""){
        var keyValueArray = qry.split("&");
        for ( var i = 0; i < keyValueArray.length; i++) {
            if(keyValueArray[i].indexOf(name)>-1){
                return keyValueArray[i].split("=")[1];
            }
        }
    }
    return "";
}

After finding this post, when looking myself I thought I should add that I don't think the most up-voted solution is the best. It doesn't handle array values (such as ?a=foo&a=bar - in this case I would expect getting a to return ['foo', 'bar']). It also as far as I can tell doesn't take into account encoded values - such as hex character encoding where %20 represents a space (example: ?a=Hello%20World) or the plus symbol being used to represent a space (example: ?a=Hello+World).

Node.js offers what looks like a very complete solutions to querystring parsing. It would be easy to take out and use in your own project as its fairly well isolated and under a permissive licence.

The code for it can be viewed here: https://github.com/joyent/node/blob/master/lib/querystring.js

The tests that Node has can be seen here: https://github.com/joyent/node/blob/master/test/simple/test-querystring.js I would suggest trying some of these with the popular answer to see how it handles them.

There is also a project that I was involved in to specifically add this functionality. It is a port of the Python standard lib query string parsing module. My fork can be found here: https://github.com/d0ugal/jquery.qeeree

function decode(s) {
    try {
        return decodeURIComponent(s).replace(/\r\n|\r|\n/g, "\r\n");
    } catch (e) {
        return "";
    }
}
function getQueryString(win) {
    var qs = win.location.search;
    var multimap = {};
    if (qs.length > 1) {
        qs = qs.substr(1);
        qs.replace(/([^=&]+)=([^&]*)/g, function(match, hfname, hfvalue) {
            var name = decode(hfname);
            var value = decode(hfvalue);
            if (name.length > 0) {
                if (!multimap.hasOwnProperty(name)) {
                    multimap[name] = [];
                }
                multimap[name].push(value);
            }
        });
    }
    return multimap;
}
var keys = getQueryString(window);
for (var i in keys) {
    if (keys.hasOwnProperty(i)) {
        for (var z = 0; z < keys[i].length; ++z) {
            alert(i + ":" + keys[i][z]);
        }
    }
}

Building on the answer by @CMS I have the following (in CoffeeScript which can easily be converted to JavaScript):

String::to_query = ->
  [result, re, d] = [{}, /([^&=]+)=([^&]*)/g, decodeURIComponent]
  while match = re.exec(if @.match /^\?/ then @.substring(1) else @)
    result[d(match[1])] = d match[2] 
  result

You can easily grab what you need with:

location.search.to_query()['my_param']

The win here is an object-oriented interface (instead of functional) and it can be done on any string (not just location.search).

If you are already using a JavaScript library this function make already exist. For example here is Prototype's version

Okay, since everyone is ignoring my actual question, heh, I'll post mine too! Here's what I have:

location.querystring = (function() {

    // The return is a collection of key/value pairs

    var queryStringDictionary = {};

    // Gets the query string, starts with '?'

    var querystring = unescape(location.search);

    // document.location.search is empty if no query string

    if (!querystring) {
        return {};
    }

    // Remove the '?' via substring(1)

    querystring = querystring.substring(1);

    // '&' seperates key/value pairs

    var pairs = querystring.split("&");

    // Load the key/values of the return collection

    for (var i = 0; i < pairs.length; i++) {
        var keyValuePair = pairs[i].split("=");
        queryStringDictionary[keyValuePair[0]] = keyValuePair[1];
    }

    // Return the key/value pairs concatenated

    queryStringDictionary.toString = function() {

        if (queryStringDictionary.length == 0) {
            return "";
        }

        var toString = "?";

        for (var key in queryStringDictionary) {
            toString += key + "=" + queryStringDictionary[key];
        }

        return toString;
    };

    // Return the key/value dictionary

    return queryStringDictionary;
})();

And the tests:

alert(window.location.querystring.toString());

for (var key in location.querystring) {
    alert(key + "=" + location.querystring[key]);
}

Mind you thought, JavaScript isn't my native tongue.

Anyway, I'm looking for a JavaScript library (e.g. jQuery, Prototype) that already has one written. :)