Javascript Querystring Replacement

QuerystringReplacement.js

    function queryStringUrlReplacement(url, param, value) 
    {
        var re = new RegExp("[\\?&]" + param + "=([^&#]*)"), match = re.exec(url), delimiter, newString;
    
        if (match === null) {
            // append new param
            var hasQuestionMark = /\?/.test(url); 
            delimiter = hasQuestionMark ? "&" : "?";
            newString = url + delimiter + param + "=" + value;
        } else {
            delimiter = match[0].charAt(0);
            newString = url.replace(re, delimiter + param + "=" + value);
        }
    
        return newString;
    }

This function will add new parameter if not exist before, and will replace the old one if exist, without messing with any of existing querystring parameters.

to use `var newUrl = queryStringUrlReplacement('http://www.tomatmerah.com/', 'page', '18');`