🈯declaration

🚧 under construction -> function*

JS ⟩ grammar ⟩ declaration

⭐️ only the following are (9) declarations：

• let / const ( ⚠️ var is a statement❗️)

• class / function,

• function*

• async function, async function*

• import / export (only appear at the top-level of a module)

⭐️ 重點

⭐ declarations and statements are different❗

👉 statement vs. declaration❗

statement vs. declaration

• var is a statement. (👉 var is a statement❗️)

• let/const is a declaration.

👉 statement expected❗️❗

in a module there's no "module scope object" for these top-level declarations to be added to as property.

( 👉 compare： global var / function is global object property❗️)

🔴 主題

• declaring variables

  • variable declaration

  • var ❗ (⭐ "var" is a statement, not a declaration❗)

  • let

  • const

  • redeclaration❗

• declaring functions

  • function declaration

  • function

    • function in block (FiB)❗

  • class

  • function*

  • async function

  • async function*

• import/export ( 👉 📘 MDN )

  • export

    Used to export functions to make them available for imports in external modules, and other scripts.

  • import

    Used to import functions exported from an external module, another script.

🧨 雷區

⭐var is a statement, not a declaration. 👉 statement expected❗️❗

👥 相關

• lexical environment - stores local variables/functions.

📗 參考

• YDKJS: Scope & Closures (v.2) ⟩ Ch. 4 ⟩ ES Modules

📘 手冊

• Statements and declarations ⟩

  • declaring variables
  • declaring functions and classes
  • Difference between statements and declarations❗️❗️❗️

🚧

• function*

• async function

• async function*