JS: Helper for dealing with url vars/params in a string

gistfile1.js

/*

Param Helper (Jed Verity 2011)

USAGE

Given query = "?foo=bar&oof=rab":

query.param('foo')          // 'bar'
query.param('oof')          // 'rab'
query.param(1)              // { key: 'foo', val: 'bar' }
query.param(2)              // { key: 'oof', val: 'rab' }
query.param()               // [{ key: 'foo, val: 'bar'}, { key: 'oof', val: 'rab' }]
query.param('foo', 'nobar') // '?foo=nobar2&oof=rab'
query.param('new')          // null
query.param('new', 'arg')   // '?foo=bar&oof=rab&new=arg'

Works the same if query = '#foo=bar&oof=rab' or query = '&foo=bar&oof=rab'

*/

String.prototype.param = function(key, value) {
    var index = parseInt(key, 10),
        re = index || !key ? '([^=]*)' : key,
        restr = '[?#&]' + re + '=([^&]*)',
        reobj = RegExp(restr, index || !key ? "g" : ''),
        match = this.match(reobj),
        result = null,
        new_val, obj, stage;

    if ( match && !value ) {
        if (index || !key) {
            obj = [];
            stage = index ? [match[index-1]] : match;
            for (var i = 0; i < stage.length; i++) {
                 new_val = stage[i].match(restr);
                 obj.push({key: new_val[1], val: new_val[2]});
            }
            result = !key ? obj : obj[0];
        } else {
            result = decodeURIComponent(match[1].replace(/\+/g, ' '));
        }
    } else if ( value ) {
        new_val = '&' + key + '=' + value;
        result = match ? this.replace(match[0], new_val) : (this + new_val) ;
    }
    return result;
};