🛡️strict mode

🚧 施工中

JS ⟩ concepts ⟩ environment ⟩ JS engine ⟩ mode ⟩ strict

🛡️ always use strict mode❗ (👉 see why)

a way to opt in to a restricted variant of JavaScript, thereby implicitly opting-out of "sloppy mode".

⭐️ 重點

in strict mode：

• duplicate parameter not allowed in strict mode❗️❗

• function in block (FiB) is local to the block.

JS is lenient with var, strict with let.

• var redeclaration applied even in strict mode❗️, even in strict mode❗

• let redeclaration not allowed even in sloppy mode❗️, even in sloppy mode❗

referencing a function in block (FiB) outside the block：

• sloppy mode: ✅ hoisted / initialized to undefined (in outer scope)

• strict mode: ⛔ ReferenceError (invisible in outer scope)❗

class / ES module always works in strict mode❗️

🔴 主題

• ✅always use strict mode

• eval has its own scope in strict mode

• var redeclaration applied even in strict mode❗️ (even in strict mode)❗

• duplicate parameter not allowed in strict mode❗️ (in strict mode)❗

👥 相關

• ⛔delete of an unqualified identifier in strict mode❗️

• ⛔octal literals not allowed in strict mode❗️

🖥️ 影片

📗 參考

• eval of strict mode code does not introduce new variables into the surrounding scope
• itHome ⟩ 你不可不知的 JavaScript 二三事 ⟩

  • #Day11：Strict Mode (嚴謹模式)
  • #Day12：看 Strict Mode 如何施展「還我漂亮拳」(1)
  • #Day13：看 Strict Mode 如何施展「還我漂亮拳」(2)

📘 手冊

• Strict mode