看别人源码碰到的，做个备忘。

//针对对象增加get\set方法，返回绑定函数的返回值Date.prototype.__defineGetter__('getYear', function() {
   return this.getFullYear();});     Date.prototype.__defineSetter__('setYear', function(year) {
   this.setFullYear(year)});Date.prototype.__defineGetter__('sayHello', function() {
   return "Hello"}); var now = new Date;     console.log(now.getYear); //2015 now.setYear  = 2011;console.log(now.getYear); //2006console.log(now.sayHello);