🔸parameter

named variable passed into function, used to import arguments.

JS ⟩ object ⟩ function ⟩ parameter

🈯 synonyms： "formal parameter", "function parameter"

a named variable passed into a function, used to import argument(s) into functions.

⭐️ 重點

⭐ in JS, arguments are passed by value❗️

⭐ function declaration instantiation - how parameters are stored.

🔴 主題

• types of parameters

  • default parameter / initial value

  • rest parameters

  • destructured parameter

  • ❗deplicate parameters ( not allowed in strict mode❗️)

  • ⚖️simple vs. non-simple parameter

• other topics

  • ⚖️parameter vs. argument

  • 🔰function overloading

  • 🔰arrow function as argument

  • 🔰function declaration instantiation - how parameters are stored.

  • 🔰parameter scope

  • ❗arguments are passed by value❗️

  • ❗var can shadow parameter even in strict mode❗️

👥 相關

• argument

• function declaration

• function expression

• function declaration instantiation - how parameters are stored.

💈範例

// ⭐️ parameters:
//   • lie in function's definition (compile-time)
function foo( param1, param2, ... ) { ... }
//           ╰─── parameters ────╯

// ⭐️ arguments:
//   • values passed into function when called (run-time)
//   • parameters are initialized to these values.
//   • can be different on each call.
foo( 1, 'hello', false );
//  ╰─── arguments ───╯

foo( 2, 'world', false );
//  ╰─── arguments ───╯

🗣 討論

• Where are arguments positioned in the lexical environment? ⭐️

📘 手冊

• Argument

• Parameter

• the "arguments" object

• SyntaxError: missing formal parameter