javaScript 工作必知(八) 属性的特性 值、写、枚举、可配置

属性的特性

"use strict";//使用严格模式
var descriptor = Object.getOwnPropertyDescriptor({ x: 1 }, "x");//获取匿名对象的值
alert("value:" + descriptor.value + "\r\n writeable:" + descriptor.writable + "\r\n enumberable:" + descriptor.enumerable + "\r\n configurable:" + descriptor.configurable);//value: 1 writeable:true enumberable:true,configurable:true

var baseDescriptor = Object.getPrototypeOf({ x: 2 });
for(var p in baseDescriptor)
{
alert(p);//内置属性不可被枚举。
}
var o = {};
Object.defineProperty(o, "y", { value: 1, writable: true, enumberable: false, configurable: true });//设置属性的特性。
var oDescriptor = Object.getOwnPropertyDescriptor(o, "y");

Object.defineProperties(o, {
x: { value: 3, writable: false, enumberable: true, configurable: true },
z: { get: function () { return this.x + 1; }, enumerable: true, configurable: true }//get表示只读属性，set可设计写属性。
});
alert(o.y);
alert("\r\n value:" + oDescriptor.value + " \r\nwritable:" + oDescriptor.writable + "\r\n enumberable:" + oDescriptor.enumerable + "\r\n configurable:" + oDescriptor.configurable);
alert(o.z);
o.x = 4;
alert(o.z);

summary