如何在JavaScript中检测全局变量何时？ [英] How can I detect when a global variable is set in javascript?

问题描述

在javascript中，我可以通过使用 Object.defineProperty 来检测何时设置全局变量 foo （假设它最初未定义） code>：

In javascript, I can detect when a global variable foo is set (assuming that it is initially undefined) by using Object.defineProperty:

var foo_;
Object.defineProperty(window, 'foo', {
  get: function() {
    return foo_;
  },
  set: function(newFoo) {
    console.log('foo set to ' + newFoo);
    foo_ = newFoo;
  }
});

有没有更优雅的方式来做到这一点？一个缺点是我不能在同一个属性两次调用 Object.defineProperty 。覆盖整个属性只是为了检测什么时候被定义似乎有点过分。

Is there a more elegant way to do this? One downside is that I cannot call Object.defineProperty on the same property twice. Overriding the entire property just to detect when it is defined seems a bit overkill.

我可以以某种方式使用代理？我觉得我必须做出一个代替目标窗口对象的代理，但是这是有效的？

Could I somehow use proxies? I feel like I would have to make a proxy that targets the window object though ... is that efficient?

推荐答案

有没有更优雅的方式呢？

Is there a more elegant way to do this?

不是真的。也许你可以（应该）隐藏 _foo ，而不是创建另一个全局变量。

Not really. Maybe you could (should) hide _foo in a closure instead of creating another global variable.

一个缺点是我不能在同一个属性两次调用 Object.defineProperty 。覆盖整个属性只是为了检测什么时候被定义似乎有点过分。

One downside is that I cannot call Object.defineProperty on the same property twice. Overriding the entire property just to detect when it is defined seems a bit overkill.

唯一的问题是你忘了传递可配置：true 选项。

The only problem is that you forgot to pass the configurable: true option.

我可以用某种方式使用代理？

Could I somehow use proxies?

不。您不能用代理替换全局对象。唯一可以做的是将所有的代码都包含在一个中（新代理（...））{...} 块。

No. You cannot replace the global object with a proxy. The only thing you could do is wrap all the code in a with (new Proxy(…)) { … } block.

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