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);
 //输出结果：
 ///one/two/four
 //http://example.com/one
 //http://example.com/two