🔑contextual keyword

🚧 施工中

JS ⟩ grammar ⟩ keyword ⟩ contextual keyword

keyword that can/cannot be used as identifier in some contexts.

// 18 contextual keywords
as async from get implements interface let of 
package private protected public set static target
await yield    // ⭐️ reserved words

• contextually allowed as identifier： (2)

  • await - reserved only inside async functions and modules.

  • yield -

• contextually disallowed as identifier, in strict mode code：(8)

  • let

  • static, implements, interface, package, private, protected, public.

• mostly allowed as identifier, but also appear as keywords within certain syntactic productions, at places where identifier is not allowed：(8)

  • as, from, get, meta, of, set, target.

  • async - can be used as a variable name or statement label without restriction.

⭐️ 重點

await, yield are reserved word and contextual keywords at the same time.

• NaN, Infinity, and undefined are：

  • not reserved keywords.

  • immutable & read-only properties of the global object.

• JavaScript does not throw any errors if you declare them in the global scope.

📗TeckTutorialHub

💈範例

• replit：reserved words

// 18 contextual keywords
as async from get implements interface let of 
package private protected public set static target
await yield    // ⭐️ reserved words

📘 手冊

• Lexical grammar ⟩ keywords ⟩ reserved words

• SyntaxError: "x" is a reserved identifier

• ECMA spec ⟩ 12.6.2 Keywords and Reserved Words ⟩ Reserved Words ⭐️

📗 參考

• TeckTutorialHub ⟩ JavaScript Keywords & Reserved Words ⭐️

🚧

• undefined

• NaN

• Infinity