📘global object

🚧 施工中

JS ⟩ scope ⟩ global ⟩ object

an object that always exists in the global scope. ⭐️ get it with globalThis, regardless of the current context/environment❗

global object's interface depends on the environment：

• in browser： window (a Window object)

• in web worker： self (a WorkerGlobalScope object)

• in Node.js：global (an object called global)

⭐️ 重點

(read-only) global object property❗

• NaN/Infinity/ undefined

in global scope,

• var / function are implemented as global object property❗

• these properties cannot be deleted with delete❗

👉 global var / function is global object property❗️

🔴 主題

• properties of global object

  • read-only

    • undefined

    • NaN 🚧

    • Infinity 🚧

  • global object property

    • accidental global variable in sloppy mode❗️

🧨 雷區

assignment (=) to an undeclared identifier will result in accidental global variable in sloppy mode❗️ in sloppy mode❗

global var / function is global object property❗️

global let shadows global object property❗

🗣 討論

• What is the 'global' object in NodeJS ⭐️

• Is there any difference between a global variable and a property of the Global Object

📗 參考

• YDKJS: Scope & Closures (v.2) >

  • Ch. 3: The Scope Chain

  • Ch. 4: Around the Global Scope

📘 手冊

• Global object

• global context

• globalThis

🚧

• NaN

• Infinity

• global

• function declarations