jmdyck
commented
4 years ago Iterators/generators should have
%IteratorPrototype%as its prototype, or in its prototype chain before any ECMAScript code runs.
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Users are free to create iterators and set the prototype to pretty much anything they like, so this can presumably only be a constraint on "built-in" iterators (i.e., iterators created by built-in functions).
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An iterator doesn't exist before any ECMAScript code runs, so it doesn't make sense to talk about its prototype chain before any ECMAScript code runs.
So I think a better way to express this invariant would be:
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When a built-in function creates an iterator, it should specify its prototype to be either
%IteratorPrototype%or some%FooIteratorPrototype%. -
Every
%FooIteratorPrototype%should have%IteratorPrototype%on its prototype chain when it's created.
Description
Iterators/generators should have
%IteratorPrototype%as its prototype, or in its prototype chain before any ECMAScript code runs.Async iterators/generators should have
%AsyncIteratorPrototype%as its prototype, or in its prototype chain before any ECMAScript code runs.Violations?
At the current point, there is nothing violating this in the 262 spec.
Rationale: Why did we have this invariant?
Make Iterator Helpers work for all built-in iterators. (initial discussion https://github.com/tc39/ecma262/pull/2045#issuecomment-664992764)