node api

url.js

var url = require('url');
var str = 'http://user:pass@host.com:8080/p/a/t/h?query=string#hash';

// parse and format
var obj = url.parse(str,true);
console.log(url.format(obj));

// resolve the browser will do 
console.log(url.resolve('http://www.google.com/users','user'));

console.log(url.resolve('http://www.google.com/users','/user'));

console.log(url.resolve('http://www.google.com/users/','user'));

console.log(url.resolve('http://www.google.com/users','user/234'));

console.log(url.resolve('http://www.google.com/users','?user=4546'));