url.resolve(from, to)

var url = require('url');
var a = url.resolve('/one/two/three', 'four') ,
b = url.resolve('http://example.com/', '/one'),
c = url.resolve('http://example.com/one', '/two');
console.log(a +","+ b +","+ c);
//輸出結果：
///one/two/four
//http://example.com/one
//http://example.com/two

Url.prototype.resolve = function(relative) {
  return this.resolveObject(urlParse(relative, false, true)).format();
};