🈯function declaration

🚧 施工中

• JS ⟩ declaration ⟩ function declaration

• JS ⟩ value ⟩ object ⟩ function ⟩ declaration

(declaration)

creates a function object and assigns it to the specified name (an identifier).

// function declarations
function  f(params) { ... }          // normal function
function* f(params) { ... }          // generator function
async function  f(params) { ... }    // async function
async function* f(params) { ... }    // async generator function

⭐️ 重點

function declaration vs. variable declaration

• function declaration is instantly fully initialized.

• variable declaration is assigned undefined initially. (👉 hoisting)

📗 JS.info ⟩ Function Declarations

function in block (FiB)

• in sloppy mode：hoisted and visible outside the block❗

• in strict mode：local to the block❗

function declaration in the global scope

• also expose themselves as global object property. 👉 global var / function is global object property❗️❗

⭐ function declaration instantiation

When an execution context is established for evaluating an ECMAScript function：

• a new Function Environment Record is created and bindings for each formal parameter are instantiated in that Environment Record.

• Each declaration in the function body is also instantiated.

• If the function's formal parameters do not include any default value initializers then the body declarations are instantiated in the same Environment Record as the parameters ❗

• If default value initializers exist, a second Environment Record is created for the body declarations ❗

• Formal parameter(s) and function(s) are initialized as part of FunctionDeclarationInstantiation. All other bindings are initialized during evaluation of the function body.

📘 JS spec ⟩ FunctionDeclarationInstantiation

🔴 主題

• function declarations

  • function

  • function*

  • async function

  • async function*

  • function redeclaration❗

  • function in block (FiB)❗

• scopes

  • function hoisting

  • function scope / function boundary

  • function declaration instantiation

  • function name scope

  • parameter scope

  • global var / function is global object property❗️❗

👥 相關

• compare： variable declaration

• function hoisting - function declarations are processed before code runs.

• simple vs. non-simple parameter - details about parameter scope.

📗 參考

• JS.info ⟩ Function Declarations

📘 手冊

• Statements and declarations ⟩ function declaration

🚧

• function*

• async function*

• function declaration instantiation