Manipulate URL Parameters.js

/*
Description:
You need to write a function ( addOrChangeUrlParameter(url, keyValueParameter) ) that can manipulate URL parameters.

It should be able to

add a parameter to an existing URL,
but also to

change a parameter if it already exists.
Example:

addOrChangeUrlParameter("www.example.com", "key=value") 
// -> 'www.example.com?key=value' (adds a parameter).

addOrChangeUrlParameter("www.example.com?key=value", "key2=value2" ) 
// -> 'www.example.com?key=value&key2=value2' (adds another parameter).

addOrChangeUrlParameter("www.example.com?key=oldValue`", "key=newValue" ) 
// ->'www.example.com?key=newValue' (changes the parameter).
*/
function addOrChangeUrlParameter (url, param) {
      url = url.replace(new RegExp(param.split('=')[0]+'=[^&]*'), param);
      return url + (url.indexOf(param) >= 0 ? '' : (url.indexOf('?')>=0?'&':'?')+param);
    }