# 词法作用域

JavaScript 采用的是词法作用域，函数的作用域在函数定义的时候就决定了。

```javascript
var value = 1;

function foo() {
    console.log(value);
}

function bar() {
    var value = 2;
    foo();
}

bar(); // 输出 1
```

分析：

**执行 foo 函数，先从 foo 函数内部查找是否有局部变量 value，如果没有，就根据书写的位置，查找上面一层的代码，也就是 value 等于 1，所以结果会打印 1。**

如果是动态作用域，才会输出2


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