javascript中的全局变量和window.variable有什么区别?

2022-01-13 00:00:00 scope attributes javascript

我正在阅读backbone.js 文档并看到很多将属性分配给窗口对象的代码:

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";

我假设存在某种不同的范围和/或对象所有权差异(窗口是所有者而不是所有者)，但我对两者之间的细节以及为什么我会使用窗口而不是使用它感兴趣.

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" 表示错字或故意全局.
  • window.foo = "bar" sets the property foo on window.
  • foo = "bar" indicates either a typo or intentionally global.

由于我必须仔细检查是否是拼写错误，我个人认为直接设置 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" 是非法赋值，因为 foo 没有被声明并且会抛出 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" 将在范围链中查找变量 foo 并用 重新分配它"bar" 如果找到的话.如果没有找到，它会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.

另外，使用 window.foo = "bar" 您只是将属性分配给对象，可以使用 delete window.foo 删除该属性.

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 invalid delete 一个变量.

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

1 在其他环境中，例如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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