浅谈JS对象添加getter与setter的5种方法(6)

(function () {
  var o = {};
  Object.defineProperties(o,{
    "a": {
      value:1,
      writable:true,//可写
      configurable:false//不可配置
      //enumerable 默认为 false 不可枚举
    },
    "b":{
      get :function(){
        return this.a;
      },
      configurable:false
    }
  });
  console.log(o.a);  //1
  o.a = 2;      //修改值成功,writable 为 true
  console.log(o.a);  //2
  Object.defineProperty(o,"a",{value:3});//同样为修改值成功
  console.log(o.a);  //3

  //将其属性 b 的属性描述符从存取描述符重新配置为数据描述符
  Object.defineProperty(o,"b",{value:3});//抛出异常,因为 configurable 为 false
})();

(function () {
  var obj = {};

  //回收同一对象,即减少内存浪费
  function withValue(value){
    var d = withValue.d ||(
      withValue.d = {
        enumerable : false,
        configurable : false,
        writable : false,
        value :null
      }
      );
    d.value = value;
    return d;
  }
  Object.defineProperty(obj,"key",withValue("static"))
})();