#### 函数的嵌套 --- - 嵌套函数不推荐使用声明式函数; > <span class="do">正确实践:</span> ```js function sum(a,b){ //... var add = function(a,b,z){ return a+b+z; } //... } ``` > <span class="dont">错误实践:</span> ```js function sum(a,b){ //... function add(a,b,z){ return a+b+z; } //... } ```