() => void 0 causes TS7011 with noImplicitAny

[avin-kavish]

() => void 0

This function is guaranteed to return undefined under any and all conditions. Why is it saying that "Function expression, which lacks return-type annotation, implicitly has an 'any' return type"? When I look at this code, I see function expression, which lacks return-type annotation will always return undefined so why do I need to annotate this with types?

[JacksonKearl]

I can't reproduce this in playground https://www.typescriptlang.org/play/?ts=3.8-Beta#code/BQSgBAvAfGBuD2BLAJmADEA or VSCode, how are you seeing the error?

[avin-kavish]

Web Storm. It's probably a web storm bug, web storm is also bugged on other typescript fronts. (It keeps auto-completing imports from @types/... and then telling me not to import from @types/... xD)

[ajafff]

You need to enable strictNullChecks for this to work as expected.
Without strictNullChecks every type can contain undefined (and undefined itself is not considered a real type). Therefore TypeScript cannot infer which type you actually meant and infers any.

[avin-kavish]

I see.

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.

[lucattelli]

If you want to return undefined, you can simply write an empty arrow function. As functions that don't return nothing actually returns undefined.

const myFunction = () => { void 0 }
myFunction(); // undefined, but caught by TS7011

const MyNewFunction = () => { }
myNewFunction() // undefined, not caught by TS7011