Object.defineProperty

  var A = {};
  Object.defineProperty(A, 'attrName', {
      set: function(val) { 
          this.__attrName__ = val; 
          console.log('A.attrName 被设置为: ', val);
      },
      get: function() { 
          console.log('A.attrName 被获取到: ', this.__attrName__);
          return this.__attrName__; }
      });
  });