JavaScript中的（for ... in）和（for ... of）语句有什么区别？ [英] What is the difference between ( for... in ) and ( for... of ) statements in JavaScript?

问题描述

我知道循环中的是什么（它遍历密钥），但是第一次听到 for ... （它迭代超过值）。对于循环，我对感到困惑。我没有得到。这是下面的代码：

I know what is for... in loop(it iterate over key), but heard the first time about for... of(it iterate over value). I am confused with for... of loop. I didn't get adject. This is the code below :

var arr = [3, 5, 7];
arr.foo = "hello";

for (var i in arr) {
   console.log(i); // logs "0", "1", "2", "foo"
}

for (var i of arr) {
   console.log(i); // logs "3", "5", "7"
    //it is does not log "3", "5", "7","hello"
}

我得到的是， for ... of 迭代属性值。那么为什么它不记录（返回）3，5，7，你好而不是3， 5，7？但 for ... in 循环迭代每个键（0，1，2，foo）。这里 for ... in 循环也迭代 foo 键。但是对于......不是迭代超过 foo 属性的值，即你好。为什么会这样？

What I got is, for... of iterates over property values. then why it doesn't log(return) "3", "5", "7","hello" instead of "3", "5", "7" ? but for... in loop iterate over each key ("0", "1", "2", "foo"). here for... in loop also iterate over foo key. but for... of not iterarte over value of foo property ie "hello".Why it is like that?

简短的故事：

这里我控制台 for ... of 循环。它应该是log 3，5，7，hello但是这里记录3，5， 7。为什么？

here i console for... of loop. it should be log "3", "5", "7","hello" but here it logs "3", "5", "7". Why ?

示例链接

推荐答案

for in 循环遍历对象的可枚举属性名称。

for in loops over enumerable property names of an object.

for （ES6中的新内容）确实使用特定于对象的迭代器 并循环生成的值。

for of (new in ES6) does use an object-specific iterator and loops over the values generated by that.

在您的示例中，数组迭代器确实产生了所有的val数组中的ues（忽略非索引属性）。

In your example, the array iterator does yield all the values in the array (ignoring non-index properties).

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