for-in JavaScript语句中的IE8错误？ [英] IE8 bug in for-in JavaScript statement?

问题描述

我想我已经在IE（IE8）处理for-in javascript语句中发现了一个错误。经过几个小时的煮沸，这是一个小例子，看起来IE特意在for-in循环中跳过任何名为toString的属性 - 无论它是在原型中还是对象的自有属性。

I think I've found a bug in IE's (IE8) handling for the for-in javascript statement. After several hours of boiling this down to a small example, it looks like IE specifically skips any property called "toString" in a for-in loop - regardless of whether it is in a prototype or is an "Own Property" of the object.

我已将测试代码：

function countProps(obj) {
    var c = 0;
    for (var prop in obj) {
        c++;
    }
    return c;
}

var obj = {
    toString: function() {
        return "hello";
    }
};

function test() {
    var o = "";
    var d = document.getElementById('output');

    o += "<br/>obj.hasOwnProperty('toString') == " + obj.hasOwnProperty('toString');
    o += "<br/>countProps(obj) = " + countProps(obj);
    o += "<br/>obj.toString() = " + obj.toString();

    d.innerHTML = o;
}

这应该产生：

obj.hasOwnProperty('toString') == true
countProps(obj) = 1
obj.toString() = hello

但在IE中，我得到：

obj.hasOwnProperty('toString') == true
countProps(obj) = 0
obj.toString() = hello

任何名为'toString'的属性的特殊外壳破坏了我的代码，试图将方法复制到Function.prototype中 - 我的自定义toString函数总是跳过。

This special casing of any property called 'toString' is wrecking havoc with my code that tries to copy methods into a Function.prototype - my custom toString function is always skipped.

有没有人知道解决方法？这是某种怪癖模式的行为 - 或只是一个BUG？

Does anyone know a work-around? Is this some sort of quirks-mode only behavior - or just a BUG?

推荐答案

是的，这是一个错误。请参阅此答案。

Yes, it is a bug. See this answer.

引用 CMS ：

另一个众所周知的JScript错误是DontEnum Bug，如果其作用域链中的对象包含一个不可枚举的属性（具有{DontEnum}属性），如果该属性在其他对象上被遮蔽，它将保持为不可枚举，例如：

Another well known JScript bug is the "DontEnum Bug", if an object in its scope chain contains a property that is not enumerable (has the { DontEnum } attribute), if the property is shadowed on other object, it will stay as non-enumerable, for example:

var dontEnumBug = {toString:'foo'}.propertyIsEnumerable('toString');

在IE上评估为false，这会在使用时导致问题for-in语句，因为不会访问属性。

It will evaluate to false on IE, this causes problems when using the for-in statement, because the properties will not be visited.

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