Using a generic type on a TypeScript function:
const func: <T extends number>() => void = () => {
const x: T = 1
}
Emits the following error:
Cannot find name 'T'. TS2304
69 | const func: <T extends number>() => void = () => {
> 70 | const x: T = 1
| ^
71 | }
How can I use generic types inside a function (and not just on its signature)?
If you want to type arrow functions, try using the implied typing method from this answer.
const func = <T extends number>(x: T) => x;
Using the alternative function notation makes that error disappear:
function func<T extends number>(): void {
const x: T = 1
}
And we instead get the following error, which makes sense:
Type '1' is not assignable to type 'T'.
'1' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'number'. TS2322
69 | export function func<T extends number>(): void {
> 70 | const x: T = 1
| ^
71 | }
const func = <T extends number>() => { const x: T = 1 }. You'll get another error, but this is already another question 🙂