I wonder how likely it is that ECMAScript would introduce its own incompatible form of enum now that TS has become so popular. With static type checking as in TS, enums are very useful, but in the more dynamic environment of JS, the benefit is much smaller. So even if there’s nothing wrong with ECMAScript using its reserved keyword in principle, it feels like a bad idea to introduce a potential source of confusion and maybe subtle bugs when so many developers now use both languages.