Repository navigation
Async function not type checking correctly #15830
Description
Activity
Hi,
As your inner function does not specify the type the type is recognized automatically form inside of the function - I just checked:
with async its
Promise<string|number>without async its
Promise<string> | Promise<number>Isn't this correct behavior?
Hi Fis (@fis-cz). The inner type is inferred to have that return type, however the outer
fnhas a return type ofPromise<number>, whichPromise<string|number>is not assignable to.Reacted by Fiswhen I do
{ const fn = (): Promise<number> => { const innerFn = async (): Promise<number> => { if (1 === 1) { return Promise.resolve('wrong type'); } else { return Promise.resolve(1); } }; // should error with `Type 'string' is not assignable to type 'number'.` return innerFn(); }; fn(); }it works correctly. Is there a reason why not to explicitly define return type of the innerFn? (ofc, it should be working correctly in both cases)
I don't always add type annotations for my function returns. I don't want it to silently fail when relying on inference.
Addressed by #15104
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.
- locked and limited conversation to collaborators
on Jun 14, 2018
TypeScript Version: 2.3.2
Code
Expected behavior:
return innerFn()should error withType 'string' is not assignable to type 'number'.Actual behavior:
return innerFn()does not error.If you remove the
asynckeyword from the async function, the program type checks as expected: