🌟global scope

JS ⟩ scope ⟩ global

(in a programming environment) the scope that contains, and is visible in, all other scopes.

🔴 主題

• global object - an object that always exists in the global scope.

  • globalThis - identifier for the global object.

  • window - global object in browser.

  • self - global object in web worker.

  • global - global object in Node.js.

  • global object property

• global variable

• DOM element with "id"

• isCurrentlyInGlobalScope() - check if current context is in global scope.

⭐️ 重點

global scope

• in browsers：global scope is top-level scope.

• in Node.js：global scope is not top-level scope.

👉 Node.js ⟩ "global" ⭐️

in the global scope, var/function declarations also expose themselves as property on the global object.

in global scope, JS exposes its built-ins:

• primitives: undefined, null, Infinity, NaN

• natives: Date, Object, String ...

• global functions: eval, parseInt()...

• namespaces: Math, Atomics, JSON ...

• friends of JS: Intl, WebAssembly ...

📗 You Don't Know JS yet

each environment puts some of its own built-ins into the global scope：

• browser：

  • console

  • DOM： window, document, ...

  • timers：setTimeout(..), ...

  • web APIs：navigator, history, geolocation, WebRTC, ...

• web worker：??? (anything else?)

• Node.js：???

A "variable" is just a property of the environment record (associated with the currently executing block /function /module /script).

Functions created with the Function constructor always are created in the global scope. 👉 MDN

🗺️ 圖表

✅ each module has its own scope

❌ global object shared by all scripts

📗 參考

• ringojs ⟩ Understanding module and global scope ⭐️

• YDKJS: Scope & Closures (v.2) ⟩

  • Ch. 3: The Scope Chain

  • Ch. 4: Around the Global Scope

📘 手冊

• Global scope

• Scope

🗣 討論

• What is the 'global' object in NodeJS