#### 函數的嵌套
---
- 嵌套函數不推薦使用聲明式函數;
> <span class="do">正確實踐:</span>
```js
function sum(a,b){
//...
var add = function(a,b,z){
return a+b+z;
}
//...
}
```
> <span class="dont">錯誤實踐:</span>
```js
function sum(a,b){
//...
function add(a,b,z){
return a+b+z;
}
//...
}
```
