我可以构造一个JavaScript对象而不使用new关键字？ [英] Can I construct a JavaScript object without using the new keyword?

问题描述

这里是我想做的：

function a() {
  // ...
}
function b() {
  //  Some magic, return a new object.
}
var c = b();

c instanceof b // -> true
c instanceof a // -> true
b instanceof a // -> true

有可能吗？我可以通过挂钩 a b 成为 a 的实例c>到它的原型链，但是我必须做 new b（），这是我想要避免的。

Is it possible? I can make b be an instance of a easily by hooking a into its prototype chain but then I have to do new b(), which is what I'm trying to avoid. Is what I want possible?

更新：我觉得使用 b .__ proto__ = a.prototype 。

更新2：下面是最接近你可以得到的，这是好的对我来说够多的了。感谢所有有趣的答案。

Update 2: Below is what seems to be the closest you can get, which is good enough for me. Thanks all for the interesting answers.

function a() {
  // ...
}
function b() {
  if (!(this instanceof arguments.callee)) {
    return new arguments.callee();
  }
}
b.__proto__ = a.prototype

var c = b();
c instanceof b // -> true
c instanceof a // -> false
b instanceof a // -> true

更新3： href =http://blog.higher-order.net/2008/02/21/javascript-parasitic-inheritance-power-constructors-and-instanceof/ =nofollow noreferrer>power constructors的博文，一旦我添加了必要的 b .__ proto__ = a.prototype 行：

Update 3: I found exactly what I wanted in a blog post on 'power constructors', once I added the essential b.__proto__ = a.prototype line:

var object = (function() {
     function F() {}
     return function(o) {
         F.prototype = o;
         return new F();
     };
})();

function a(proto) {
  var p = object(proto || a.prototype);
  return p;
}

function b(proto) {
  var g = object(a(proto || b.prototype));
  return g;
}
b.prototype = object(a.prototype);
b.__proto__ = a.prototype;

var c = b();
c instanceof b // -> true
c instanceof a // -> true
b instanceof a // -> true
a() instanceof a // -> true

推荐答案

您可以使用此模式：

function SomeConstructor(){
   if (!(this instanceof SomeConstructor)){
        return new SomeConstructor();
   }
   //the constructor properties and methods here
}

之后你可以做：

var myObj = SomeConstructor();

除了这个（相当老的）答案：你可以使用 模块模式 创建对象：

In addition to this (rather old) answer: you can use a module pattern to create an object:

function Person(name, age, male) {
  name = name || 'unknown';
  age = age || 0;
  function get() {
    return ['This person is called ', name,
            (!male ? ', her' : ', his'),' age is ',
            age].join('');
  }
  function setAge(nwage) {
     age = nwage;
  }
  return Object.freeze({get: get, setAge: setAge});
}
// usage
var jane =  Person('Jane', 23)
   ,charles = Person('Charles', 32, 1)
   ,mary = Person('Mary', 16);

console.log(jane.get()); //=> This person is called Jane, her age is 23
mary.setAge(17);
console.log(jane.get()); //=> This person is called Mary, her age is 17

这是一个 jsFiddle 某些日期 。

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