js对象，set和get方法 的三种实现形式

   var obj1 = {
         name: 'shaanxi',
         get nameGet() {
             return this.name + 'a';
         },
         set nameSet(name) {
             this.name = name;
         }
     };

     console.info(obj1.nameGet);  //shaanxia
     obj1.nameSet = 'set by set keywords';
     console.info(obj1.nameGet);  //set by set keywordsa

第一种方式，直接在对象内设置。如代码所示。

   var obj2 = {
         name: 'shaanxi'
     };

     obj2.__defineGetter__('nameGet', function() {
         return this.name;
     });
     obj2.__defineSetter__('nameSet', function(
         name) {
         this.name = name;
     });
     var ref1 = obj2.__lookupGetter__('nameGet');
     var ref2 = obj2.__lookupSetter__('nameSet');
     console.info(obj2.nameGet);  //shaanxi
     obj2.nameSet = 'set by __defineSetter__';
     console.info(obj2.nameGet);  //set by __defineSetter__

第二种方式：使用原型方法进行设置

  var obj3 = {
         name: "shaanxi"
     };
  Object.defineProperties(obj3, {
         nameGet: {
             value: function() {
                 return this.name;
             }
         },
         nameSet: {
             value: function(name) {
                 this.name = name;
             }
         }
     });

     console.info(obj3.nameGet());  //shaanxi
     obj3.nameSet('set by Object.defineProperty');
     console.info(obj3.nameGet());  //set by Object.defineProperty

第三种方式：使用Object.defineProperty()和Object.defineProperties()进行设置