⛔identifier 'xxx' has already been declared❗️

JS ⟩ error ⟩ SyntaxError ⟩ identifier 'xxx' has already been declared

⛔ SyntaxError: identifier 'xxx' has already been declared

✨ 範例

• var has no block scope❗️⛔

• var in block can't shadow outer let❗️⛔

• let redeclaration not allowed even in sloppy mode❗️⛔

📗 參考

• YDKJS: Scope & Closures (v.2) ⟩ Ch. 1: What's the Scope?