Get query string argument (using split/for)

getqueryarg-splitfor.js

/**
 * Returns specified argument from query string.
 *
 * @params  {string} key - Argument to be returned.
 * @returns {string} Value of key ('' for ?arg=, null for ?arg, undefined if not present).
 */
function getQueryArg(key) {
    var srch = location.search.substring(1);  // lose the initial '?'
    var args = srch.split(/[&;]/);            // list of field=value pairs
    for (var i=0; i<args.length; i++) {       // for each arg
        var arg = args[i].split('=');         // split at '='
        if (arg[0] == key) {                  // arg we're looking for?
            if (arg.length == 1) return null; // ?key without '='
            return decodeURIComponent(arg[1].replace(/\+/g, ' '));
        }
    }
    return undefined;                         // not found
}