使用Object.defineProperty为对象定义属性

var demo = {
    foo:1,
    bar:2
};
Object.defineProperty(demo, 'foo',{
    value:100
});
Object.defineProperty(demo, 'foobar',{
    value:"hello"
});

Object.defineProperty(demo, 'foobar',{
    value:"hello",
    enumerable:false
});

var o = {};
Object.defineProperty(o, "a", { value : 1, enumerable:true });
Object.defineProperty(o, "b", { value : 2, enumerable:false });
Object.defineProperty(o, "c", { value : 3 }); // enumerable defaults to false
o.d = 4; // 如果使用直接赋值的方式创建对象的属性，则这个属性的enumerable为true

for (var i in o) {    
  console.log(i);  
}
// 打印 'a' 和 'd' (in undefined order)

Object.keys(o); // ["a", "d"]

o.propertyIsEnumerable('a'); // true
o.propertyIsEnumerable('b'); // false
o.propertyIsEnumerable('c'); // false

var demo = {
  foobar: 'hello'
}
var v;
Object.defineProperty(demo,'foobar',{
  get:function(){
    console.log('i am been getting')
    return v + '?'
  },
  set:function(e){
    v = e + '!';
    console.log('i am changing!')
  }
  }
)
demo.foobar = "bye"
console.dir(demo.foobar)
//'i am changing!'
//'i am been getting'
//'bye!?'

var demo = {}

var v;
Object.defineProperty(demo,'foobar',{
  get:function(){
    return v;
  },
  set:function(e){
    v = e;
    sow();
  }}
);

function sow(){
   $('body').html(demo.foobar) 
}


demo.foobar = "hello"

setTimeout(function(){
  demo.foobar = "bye"
  setTimeout(function(){
      demo.foobar = 'i am back'
  },1000) 
},1000)