⚖️identifier vs. keyword

JS ⟩ identifier ⟩ vs. keyword

there are 5 categories of identifier names:

• not keywords (always allowed as identifiers)： Math, window, toString, _ ...

• keywords：

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

  • contextually allowed as identifiers： namely await, yield.

  • contextually disallowed as identifiers, in strict mode code:： let, static, implements, interface, package, private, protected, public.

  • always allowed as identifiers, but also appear as keywords within certain syntactic productions, at places where identifier is not allowed: as, async, from, get, meta, of, set, target

The term conditional keyword, or contextual keyword, is sometimes used to refer to the keywords that fall in the last 3 categories, and thus can be used as identifiers in some contexts and as keywords in others. 📘ECMA

📘 手冊

• Lexical grammar ⟩

  • keywords

  • Identifier