为什么我不能覆盖`Array`(Array.prototype`)的原型? [英] Why can't I overwrite the prototype of `Array` (`Array.prototype`)?
问题描述
我将 Array 的原型设置为 my 的实例，我认为 book.aa 将显示"aa" ，但显示"undefined" ，为什么?谢谢！
I set the prototype of Array as an instance of my, I think book.aa will display "aa", but it displays "undefined", why? Thanks!
<html>
<head>
<title>Array Properties</title>
<h2>Array Properties</h2>
<script type="text/javascript">
function my() {
this.aa = 'aa';
}
Array.prototype = new my();
Array.prototype.bb = "bb";
var book = new Array();
book[0] = "War and Peace";
</script>
</head>
<body bgcolor="lightblue">
<script type="text/javascript">
document.write(book.aa+book.bb);
</script>
</body>
</html>
推荐答案
您无法分配给 Array.prototype ，因为 prototype 是的只读属性数组.
You cannot assign to Array.prototype because prototype is a read-only property of Array.
所以当你写
Array.prototype = new my();
什么都没有发生.要了解原因，请尝试
nothing happens. To see why, try
JSON.stringify(Object.getOwnPropertyDescriptor(Array, "prototype"))
结果是
"{"value":[],"writable":false,"enumerable":false,"configurable":false}"
除非您处于严格模式，否则分配将自动失败.
Unless you are in strict mode, the assignment silently fails.
这就是原因-如果执行，请参阅 http://jsfiddle.net/5Ysub/
That's why -- and see http://jsfiddle.net/5Ysub/ -- if you execute
function my() {
this.aa = 'aa';
}
Array.prototype = new my();
Array.prototype.bb = "bb";
var book = new Array();
book[0] = "War and Peace";
document.write(book.aa+book.bb);
你得到
undefinedbb
bb 之所以有效，是因为您在创建并设置 bb real Array.prototype >属性.
The bb works because you have assigned to the real Array.prototype when you created and set the bb property.
恕我直言，不能对 Array.prototype 进行黑客攻击是一件好事.:)
It is a good thing that Array.prototype cannot be whacked, IMHO. :)
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