input: "$filter=&$top=3&$skip=3&$orderby=firstName&$format=json&$inlinecount=allpages output: Object {$filter: "", $top: "3", $skip: "3", $orderby: "firstName", $format: "json"…} $callback: "callback" $filter: "" $format: "json" $inlinecount: "allpages" optional: enter key name as 2nd parameter to just get that value

getQueryString.js

$.extend({      
        getQueryString: function ( urlString, 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 = urlString;

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

                return params;
            }

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

            return key ? this.queryStringParams[key] : this.queryStringParams;
        }
    });

Using regex for this is just wrong and will fail in some scenarios.

You'd better off using a tiny reusable module like:
https://github.com/sindresorhus/query-string