Microsoft/TypeScript
Surprising `Not all code paths return a value`
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#18 319 ouverte le 7 sept. 2017
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Description
TypeScript Version: 2.5.2
Code
type AsyncFunction<T> = () => Promise<T>;
const f: AsyncFunction<number | void> = async () => {
if (Math.random()) {
return 1;
}
};
Expected behavior:
No tsc errors.
Actual behavior:
const f: AsyncFunction<number | void> = async () => {
// ~~~~~~~~~~~~~ [ts] Not all code paths return a value.
if (Math.random()) {
return 1;
}
};
Notably, when using return-type annotation, this error does not occur:
async function a(): Promise<number | void> {
if (Math.random()) {
return 1;
}
}
const b = async (): Promise<number | void> => {
if (Math.random()) {
return 1;
}
};
In our real-world scenario, it would not be sufficient to look for this syntactic pattern. Rather, the fact that the async function is assigned to a union containing void should be the trigger that silences this error.