__defineGetter__ && __defineSetter__

//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); //2006

console.log(now.sayHello);