Microsoft/TypeScript
Auf GitHub ansehentype predicate-ness lost when using Function.prototype.bind
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#29.531 geöffnet am 22. Jan. 2019
Domain: lib.d.tsExperience EnhancementHelp WantedSuggestion
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Beschreibung
TypeScript Version: 3.2.4 or @next as of 2019-01-22
Search Terms:
Code
const isArray: typeof Array.isArray = Array.isArray.bind(Array);
Expected behavior: Compiles.
Actual behavior:
Error message:
error TS2322: Type '(arg: any) => boolean' is not assignable to type '(arg: any) => arg is any[]'.
Signature '(arg: any): boolean' must be a type predicate.
What seems to be happening is that the type predicate-ness of Array.isArray is lost when .bind is used. I tested with a few type predicate functions, and always get the same error.
Playground Link:
Not reproducible on playground, because it depends on a higher TS version.
In the playground, the type of the RHS is any, so there is no compilation error.
Related Issues:
-
Typings for
Function.prototype.bindwere discussed in https://github.com/Microsoft/TypeScript/issues/212 but I couldn't find any mention of type predicates.