🗝️keyword

🚧 施工中

JS ⟩ grammar ⟩ token ⟩ keyword

A keyword is a token that matches IdentifierName (looks like an identifier), but also has a syntactic use. (📘ECMA )

// 54 keywords
as async await break case catch class const continue 
debugger default delete do else enum export extends 
false finally for from function get 
if implements import in instanceof interface 
let meta new null of package private protected public return 
set static super switch target this throw true try typeof 
var void while with yield

⭐️ 重點

keywords can be divided into：

• reserved word： never allowed as identifier (except await, yield)

• contextual keyword：

  • contextually allowed as identifier： namely await, yield.

    • await - reserved only inside async functions and modules.

  • contextually disallowed as identifier, in strict mode code:： 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: as, async, from, get, meta, of, set, target.

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

NaN/Infinity/ undefined is：

• not keyword.

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

• JS doesn't throw any errors if you declare them in the global scope.

📗TeckTutorialHub

• avoid using reserved word as identifiers (at least for variable/function) ❗

• in dot notation (.), it's OK to use reserved word as property name❗

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