🔰function hoisting

identifier hoisted at top of scope, value initialized to a function value (instantly).

JS ⟩ scope ⟩ hoisting ⟩ function hoisting

with a function declaration：

• identifier： hoisted to the top of its scope.

• value： initialized to a function value (instantly).

referencing a function in block (FiB) outside block

• sloppy mode: ✅ hoisted / initialized to undefined (outside block)

• strict mode: ⛔ ReferenceError (invisible outside block)❗

🔴 主題

• related topics

  • function declaration

⭐️ 重點

function declaration(s)

• are processed before code runs (at compile-time) so it seems that they are "hoisted" to the top of their scope.

in the same scope, function hoisting has higher priority over variable hoisting. ( 👉 function hoisting first❗️❗)

👥 相關

• compare：function expression not hoisted

• variable hoisting / var hoisting / let/const/class hoisting

💈範例

• replit：function hoisting

// function declarations can be called from the start
greeting();                        // Hello!

// ⭐️ function hoisting
// ------------------------------------------------------
// • applies to "function declarations" only.
// • identifier: (function name) hoisted to top of scope.
// • value     : initialized (to a function value).
// ------------------------------------------------------
function greeting() {
    console.log("Hello!");
}

📗 參考

• YDKJS: Scope & Closures (v.2) ⟩

  • Ch. 1 ⟩ Hoisting

  • Ch. 5 ⟩ Hoisting: Declaration vs. Expression