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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
                # let - const 命令總結 --- ## 1.共同點 - 不存在變量提升 - 不可重復聲明(一個代碼塊內,父子作用域不相干)! - 聲明的變量只會存在全局或者作用域塊范圍內(不會掛載到全局 this 下) > 示例: ![](https://box.kancloud.cn/91e637235b74ad6de9d6ebea468137d9_554x131.jpg) ## 2.let > 示例: ``` function letTest(){ let x = 1 if(true){ let x = 2 console.log(x) // 2 } console.log(x) // 1 不存在變量提升因此子代碼塊中聲明的X不會覆蓋掉上層代碼塊中聲明的X變量 } ``` ## 3.const - 定義時必須賦值 - 不可更改直接值(若定義為對象則不可更改類型,但可以對對象內部屬性和值的引用進行增改,數組同上)
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