英文:

global variable in Node.js: weird behaviour

问题

我有下面几个JavaScript文件：

homeFunction.js:
```javascript
const { testFunc2 } = require("./TestFunction");

function home(val) {
    global.context = {};
    global.context.val = val;
}

home(3);
testFunc2();

下面是TestFunction.js：

exports.testFunc2 = () => {
    console.log(context.val);
}

这段代码输出3，尽管在testFunc2之前我没有使用global关键字来声明context。这是如何运作的呢？我猜测Node.js会在局部作用域中查找名为context的变量，如果在局部找不到，它会继续查找全局作用域。这个猜测正确吗？

谢谢！

<details>
<summary>英文:</summary>

I have below couple of files of javascript:

const { testFunc2 } = require("./TestFunction");

function home(val){
global.context={};

global.context.val = val;

}

home(3);
testFunc2();
//homeFunction.js

Below is `TestFunction.js`:

exports.testFunc2=()=>{
console.log(context.val);
}

This code prints 3 as the output, even though I have not put ``global`` before ``context`` in testFunc2. How does this actually works? My guess is that node looks for a variable named context in local scope, if it is not able to find it local, it moves onto global scope. Is that correct?

Thanks!

</details>


# 答案1
**得分**: 1

是的，明确的 `global` 对象是 Node.js 的一个独特特性。这是一个在 Node.js 程序中所有模块之间**共享**的对象，即使你没有积极采取任何操作来引起共享（正如你所说）。

如果没有名为 `context` 的局部变量，你对 `context` 的引用将会落到全局的 `context` 上，你可以使用 `global.context=` 来写入它。

在某种程度上，这类似于在浏览器中写入 `window.xyz`，然后导入一个尝试读取 `xyz` 的模块时会发生的情况。

<details>
<summary>英文:</summary>

### Yes, the explicit `global` object is a feature peculiar to Node JS

It is an object that is _shared_ between all the modules in a Node JS program, even when you don&#39;t feel like you are actively doing anything to cause the sharing (as you say).

If there is no local variable called `context`, your reference to `context` falls through to the global `context`, which you wrote into using `global.context=`.

In a way, it is similar to what would happen in a browser if you wrote to `window.xyz` and then imported a module that tried to read `xyz`. 

</details>