前端一些知識點整理

原創 香辣素毛肚 2020-06-09 22:53

執行環境和作用域

執行環境

每一個函數都是一個執行環境，函數A裏面定義的函數B，則A就是B的父環境，B可以訪問A中定義的變量，A不能訪問B內的變量。最外層的執行環境，對於瀏覽器而言，就是window，也就是全局執行環境。

作用域

當代碼在一個環境中執行，會創建變量對象的作用域鏈。訪問該變量，從作用域鏈最前端開始找。一直到最外層的全局執行環境。

延長作用域

在作用域鏈最前端臨時增加變量對象，代碼執行完畢後移除。

更改作用域

用call()或者apply()函數

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