“ void 0”是什么意思？ [重复]

本文翻译自：What does `void 0` mean? [duplicate]

This question already has answers here : 这个问题已经在这里有了答案：

Closed 8 years ago . 8年前关闭。

Possible Duplicate: 可能重复：
What does “javascript:void(0)” mean? “ javascript：void（0）”是什么意思？

Reading through the Backbone.js source code, I saw this: 通过阅读Backbone.js源代码，我看到了以下内容：

validObj[attr] = void 0;

What is void 0 ? 什么是void 0 ？ What is the purpose of using it here? 在这里使用它的目的是什么？

#1楼

参考：https://stackoom.com/question/VGh3/void-是什么意思-重复

#2楼

void is a reserved JavaScript keyword. void是保留的JavaScript关键字。 It evaluates the expression and always returns undefined . 它计算表达式并始终返回undefined 。

#3楼

What does `void 0` mean? `void 0`是什么意思？

void ^[MDN] is a prefix keyword that takes one argument and always returns undefined . void ^[MDN]是带一个参数的前缀关键字，始终返回undefined 。

Examples 例子

void 0
void (0)
void "hello"
void (new Date())
//all will return undefined

What's the point of that? 有什么意义呢？

It seems pretty useless, doesn't it? 看起来很没用，不是吗？ If it always returns undefined , what's wrong with just using undefined itself? 如果它总是返回undefined ，那么仅使用undefined本身undefined什么问题呢？

In a perfect world we would be able to safely just use undefined : it's much simpler and easier to understand than void 0 . 在一个完美的世界中，我们将能够安全地使用undefined ：与void 0相比，它更容易理解。 But in case you've never noticed before, this isn't a perfect world , especially when it comes to Javascript. 但是，如果您以前从未注意到过， 这不是一个完美的世界 ，尤其是在涉及Javascript时。

The problem with using undefined was that undefined is not a reserved word ( it is actually a property of the global object ^[wtfjs] ). 使用undefined的问题是undefined不是保留字（它实际上是全局对象^[wtfjs]的属性）。 That is, undefined is a permissible variable name, so you could assign a new value to it at your own caprice. 也就是说， undefined是允许的变量名，因此您可以按自己的意愿为它分配一个新值。

alert(undefined); //alerts "undefined"
var undefined = "new value";
alert(undefined) // alerts "new value"

Note: This is no longer a problem in any environment that supports ECMAScript 5 or newer (ie in practice everywhere but IE 8), which defines the undefined property of the global object as read-only (so it is only possible to shadow the variable in your own local scope). 注意：在任何支持ECMAScript 5或更高版本的环境（即，除IE 8之外，实际上在所有地方都可以使用）中，这不再是问题，该环境将全局对象的undefined属性定义为只读（因此，只能对变量进行阴影处理）在您自己的本地范围内）。 However, this information is still useful for backwards-compatibility purposes. 但是，此信息对于向后兼容的目的仍然有用。

alert(window.hasOwnProperty('undefined')); // alerts "true"
alert(window.undefined); // alerts "undefined"
alert(undefined === window.undefined); // alerts "true"
var undefined = "new value";
alert(undefined); // alerts "new value"
alert(undefined === window.undefined); // alerts "false"

void , on the other hand, cannot be overidden. 另一方面， void不能被覆盖。 void 0 will always return undefined . void 0将始终返回undefined 。 undefined , on the other hand, can be whatever Mr. Javascript decides he wants it to be. 另一方面， undefined可以是Javascript先生决定的任何类型。

Why `void 0` , specifically? 为什么`void 0` ？

Why should we use void 0 ? 为什么要使用void 0 ？ What's so special about 0 ? 0什么特别之处？ Couldn't we just as easily use 1 , or 42 , or 1000000 or "Hello, world!" 我们不能像1或42或1000000或"Hello, world!"那样轻松地使用它"Hello, world!" ? ？

And the answer is, yes, we could, and it would work just as well. 答案是，是的，我们可以，而且效果也很好。 The only benefit of passing in 0 instead of some other argument is that 0 is short and idiomatic. 传递0而不是其他参数的唯一好处是0简短且惯用。

Why is this still relevant? 为什么这仍然有意义？

Although undefined can generally be trusted in modern JavaScript environments, there is one trivial advantage of void 0 : it's shorter. 尽管在现代JavaScript环境中通常可以信任undefined ，但void 0有一个琐碎的优点：它更短。 The difference is not enough to worry about when writing code but it can add up enough over large code bases that most code minifiers replace undefined with void 0 to reduce the number of bytes sent to the browser. 这种差异不足以在编写代码时担心，但可以在大型代码库上加起来，大多数代码压缩器将undefined替换为void 0以减少发送到浏览器的字节数。

#4楼

void 0返回undefined且不能覆盖，而undefined可以覆盖。

var undefined = "HAHA";