Javascript中for..in循环的迭代顺序 [英] Iteration order of for..in loops in Javascript

问题描述

假设我有一个初始化的Javascript对象

Suppose I have a Javascript object which is initialized

var letters = {q:0, t:0, o:0, b:0, y:0, n:0, u:0, m:0, p:0, 
               w:0, a:0, d:0, k:0, v:0, c:0, z:0, l:0, j:0, 
               i:0, e:0, g:0, s:0, x:0, r:0, h:0, f:0};

然后我想迭代这个对象的键

and then I want to iterate over the keys of this objects

for(var letter in letters) {
    // code goes here
}

在Firefox 3和Internet Explorer 8中，对象按对象声明（q，t，o，b， y等。）

In both Firefox 3 and Internet Explorer 8 the objects are iterated over in the order in which they are listed in the object declaration (q, t, o, b, y, etc).

我能依靠吗？假设在迭代之前我没有以任何方式修改我的对象。它是ECMAScript标准的一部分吗？有谁知道哪些浏览器按声明的顺序迭代？

Can I rely on this? Assume that I don't modify my object in any way before the iteration. Is it part of the ECMAScript standard? Does anyone know which browsers iterate in the declared order?

推荐答案

不，它不能依赖，至少不在Firefox 中：

No, it cannot be relied upon, at least not in Firefox:

A for ... in循环以任意顺序迭代对象的属性。

A for...in loop iterates over the properties of an object in an arbitrary order.

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