Set URL Parameters.js

String.prototype.getParams = function (search) {
	var params       = null;
  	var paramsObject = new Object();
  
  	if(search && search != ""){
  		params = this.substr(this.indexOf(search) + search.length + 1, this.length);
    
  		return params.substr(0, ((params.indexOf("&") == "-1") ? params.length : params.indexOf("&")));
  	}
  
  	params = this.substr(this.indexOf("?") + 1, this.length).split("&");
  
  	for(i=0; i < params.length; i++){
  		param = params[i].split("=");
  		paramsObject[param[0]] = param[1];
  	}
  
  	return paramsObject;
};

String.prototype.setParams = function (params) {
	if(typeof(params) == "object"){
		var newurl = this;

		for(var key in params){
			if(newurl.indexOf("&" + key) != "-1"){
				newurl = newurl.replace("&" + key + "=" + newurl.getParams(key), "&" + key + "=" + params[key]);
			}else if(newurl.indexOf("?" + key) != "-1"){
				newurl = newurl.replace("?" + key + "=" + newurl.getParams(key), "?" + key + "=" + params[key]);
			}else if(newurl.indexOf("?") != "-1"){
				newurl += "&" + key + "=" + params[key];
			}else{
				newurl += "?" + key + "=" + params[key];
			}
		}	

		return newurl;
	}
};

var url = "http://www.google.de?hl=en&test=1&why=because";
var params = new Object();
params["hl"] = "de";
params["test"] = 2;
params["newparam"] = "a";
var newurl = url.setParams(params);
console.log(newurl); // http://www.google.de?hl=de&test=2&why=because&newparam=a