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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                # 作用域 > 可訪問變量的集合(對象、函數) > 我們定義了一個變量,這個變量可以被使用的地方,可以使用的范圍 # 函數 > 全局作用域(全局變量):在函數外定義,在所有地方都能被訪問 > 局部作用域(局部變量):在哈數里面定義的變量,只能在函數里面被訪問 # 作用域的工作模式 ![](https://box.kancloud.cn/e96b614047c48eb03681069ae6ecc74e_278x120.jpg) ## 題目一 ``` <script> console.log(a); //function a() {console.log(4);} var a = 1; console.log(a); //1 function a(){console.log(2)}; console.log(a); //1 var a = 3; console.log(a); //3 function a() {console.log(4);} console.log(a); //3 a(); //錯誤: a is not a function </script> ``` ![](https://box.kancloud.cn/71c8e1331af417affc1210ccc6933db5_249x120.jpg) ## 題目二 ``` var a = 1; function fn1(a) { console.log(a); a = 2; } fn1(); console.log(a); ``` 等同于如下 ``` var a = 1; function fn1(a) { console.log(a); a = 2; } fn1(); console.log(a); ``` > 結果:undefined > 1 ## 題目三 ``` var a = 1; function fn1() { console.log(a); //1 a = 2; } fn1(); console.log(a);//2 ``` ![](https://box.kancloud.cn/ee38bd3fee34460c65db85fedb6f58b1_751x358.png)
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                              哎呀哎呀视频在线观看