Object.defineProperties()

概述

Object.defineProperties() 方法在一个对象上添加或修改一个或者多个自有属性，并返回该对象。

语法

Object.defineProperties(obj, props)

参数

obj

将要被添加属性或修改属性的对象

props

该对象的一个或多个键值对定义了将要为对象添加或修改的属性的具体配置

例子

var obj = {};
Object.defineProperties(obj, {
  "property1": {
    value: true,
    writable: true
  },
  "property2": {
    value: "Hello",
    writable: false
  }
  // 等等.
});
alert(obj.property2) //弹出"Hello"

兼容旧环境（Polyfill）

下面用 JavaScript 实现的 defineProperties 函数几乎完全等价于原生的 Object.defineProperties。

function defineProperties(obj, properties)
{
  function convertToDescriptor(desc){
    function hasProperty(obj, prop){
      return Object.prototype.hasOwnProperty.call(obj, prop);
    }

    function isCallable(v){
      // 如果除函数以外,还有其他类型的值也可以被调用,则可以修改下面的语句
      return typeof v === "function";
    }

    if (typeof desc !== "object" || desc === null)
      throw new TypeError("不是正规的对象");

    var d = {};
    if (hasProperty(desc, "enumerable"))
      d.enumerable = !!desc.enumerable;
    if (hasProperty(desc, "configurable"))
      d.configurable = !!desc.configurable;
    if (hasProperty(desc, "value"))
      d.value = desc.value;
    if (hasProperty(desc, "writable"))
      d.writable = !!desc.writable;
    if (hasProperty(desc, "get")){
      var g = desc.get;
      if (!isCallable(g) && g !== "undefined")
        throw new TypeError("bad get");
      d.get = g;
    }
    if (hasProperty(desc, "set")){
      var s = desc.set;
      if (!isCallable(s) && s !== "undefined")
        throw new TypeError("bad set");
      d.set = s;
    }

    if (("get" in d || "set" in d) && ("value" in d || "writable" in d))
      throw new TypeError("identity-confused descriptor");

    return d;
  }

  if (typeof obj !== "object" || obj === null)
    throw new TypeError("不是正规的对象");

  properties = Object(properties);
  var keys = Object.keys(properties);
  var descs = [];
  for (var i = 0; i < keys.length; i++)
    descs.push([keys[i], convertToDescriptor(properties[keys[i]])]);
  for (var i = 0; i < descs.length; i++)
    Object.defineProperty(obj, descs[i][0], descs[i][1]);

  return obj;
}

规范

浏览器兼容性

基于Kangax's compat tables.

相关链接

• Object.defineProperty()
• Object.keys()
• Enumerability and ownership of properties