javascript - 揭示原型(prototype)模式不适用于 Array

Question

它在我写的时候起作用(http://jsfiddle.net/XJwvP/):

var Person = function(name) { this.name = name; }
Person.prototype = function () {
   var sayHello = function (name) {
         alert("Hello, " + name);
   };

   return {
      sayHello: sayHello
   };
}();

var person = new Person("Max");
person.sayHello("James");

当我写的时候它不起作用( http://jsfiddle.net/ZKd4R/ ):

Array.prototype = function () {
   var sayHello = function (name) {
         alert("Hello, " + name);
   };

   return {
      sayHello: sayHello
   };
}();

var array = new Array();
array.sayHello("James");

错误:

Uncaught TypeError: Object [object Array] has no method 'sayHello' 

为什么我不能对 Array 对象使用相同的方法？

Answer 1

像你一样替换 Array.prototype 不会影响新的 Array 实例，因为 Array 构造函数在语言中是特殊的(它是内置构造函数)。规范说明在 15.4.2.1 :

The [[Prototype]] internal property of the newly constructed object is set to the original Array prototype object, the one that is the initial value of Array.prototype (15.4.3.1).

如果你勾选15.4.3.1 ，你会注意到 Array.prototype 也不是 [[Writable]]。我刚刚在 Chrome 控制台中测试了它:

var ap = Array.prototype;
Array.prototype = {};
ap == Array.prototype; // true