getQueryString.js

/**
 * Get the value of a query string from a URL
 * @param  {String} field The field to get the value of
 * @param  {String} url   The URL to get the value from [optional]
 * @return {String}       The value
 */
var getQueryString = function ( field, url ) {
    var href = url ? url : window.location.href;
    var reg = new RegExp( '[?&]' + field + '=([^&#]*)', 'i' );
    var string = reg.exec(href);
    return string ? string[1] : null;
};

// http://example.com&this=chicken&that=sandwich
var thisOne = getQueryString( 'this' ); // returns 'chicken'
var thatOne = getQueryString( 'that' ); // returns 'sandwich'
var anotherOne = getQueryString( 'another' ); // returns null
var yetAnotherOne = getQueryString( 'example', 'http://another-example.com&example=something' ); // returns 'something'