javascript 中的全局变量和 window.variable 有什么区别? [英] What's the difference between a global var and a window.variable in javascript?

问题描述

我正在阅读backbone.js文档，看到了很多为window对象分配属性的代码:

I'm reading the backbone.js documents and seeing a lot of code that assigns attributes to the window object:

window.something = "whatever";

调用此代码与仅分配变量并创建全局变量有什么区别，如下所示:

what's the difference between calling this code, and just assigning the variable and creating a global var, like this:

something = "whatever";

我认为存在某种范围不同和/或对象所有权差异(窗口是所有者与不是所有者)，但我对两者之间的细节以及为什么我会使用窗口与不使用它感兴趣.

i assume there is some kind of scope different, and/or object ownership difference (window being the owner vs not) but i am interested in the detail between the two and why i would use window vs not use it.

推荐答案

没有区别.它们都具有相同的效果(在浏览器中，window 是全局上下文¹).

No difference. They both have the same effect (In the browser, where window is the global context¹).

• window.foo = "bar" 在 window 上设置属性 foo.
• foo = "bar" 表示打字错误或故意全局的.

• window.foo = "bar" sets the property foo on window.
• foo = "bar" indicates either a typo or intentionally global.

因为我必须仔细检查它是否是一个错字，我个人觉得直接设置 window.foo 更可读.

Since I have to double check whether it's a typo or not, I personally find it more readable to set window.foo directly.

另外，在 ES5 严格模式下，foo = "bar" 是一个非法赋值，因为 foo 没有被声明并且会抛出一个 Error.

Also, in ES5 strict mode, foo = "bar" is an illegal assignment because foo is not declared and will throw a Error.

如注释中所述，foo = "bar" 将在变量 foo 的作用域链上一直向上查找，并用 重新分配它bar" 如果找到了.如果没有找到，它将创建一个新的全局变量.

As noted in the comments, foo = "bar" will look all the way up the scope chain for the variable foo and re-assign it with "bar" if it's found. If it's not found, it will create a new global variable.

同样使用 window.foo = "bar" 你只是为一个对象分配一个属性，它可以使用 delete window.foo 删除.

Also with window.foo = "bar" you're just assigning a property to an object, which can be deleted using delete window.foo.

在 ES5 严格模式下，删除变量是无效.

In ES5 strict mode it is invalid to delete a variable.

¹ 在其他环境中，比如 node.js 和 Web Workers，全局对象可能有另一个名称，而 window 可能根本不存在.Node.js 使用 global，而 Web Workers 使用 self.

¹ In other environments, such as node.js and Web Workers, there may be another name for the global object and window may not exist at all. Node.js uses global and Web Workers use self.

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