typescript callback with generic function

Question

I have the following code:

type callbackType = <T>(d: T) => void;

const callbackTest = <T>(val: T, callback: callbackType) => {
    callback(val);
};

callbackTest("Hey", isAString => isAString)

Here I would expect Typescript to deduce that isAString has the type string, which it doesn't.

if i inline the callbackType like so:

const callbackTest = <T>(val: T, callback: (d: T) => void) => {
    callback(val);
};

callbackTest("Hey", isAString => isAString)

Typescript can deduce that isAString has the type string.

I Tryed adding a <T> behind callbackType (callback: callbackType<T>), but this doesn't seem to be valid Typescript and gives the following error: Type 'callbackType' is not generic.

In my real code callbackType is a more complex function that I use multiple times, therefore inlining it wouldn't be ideal.

Any ideas how I could help Typescript figure out the type of isAString?

k.tten · Accepted Answer · 2022-05-20 16:03:00Z

2

Move the generic to the type from the function:

type callbackType<T> = (d: T) => void;

Then you can pass T to the type like you originally tried:

const callbackTest = <T>(val: T, callback: callbackType<T>) => {
    callback(val);
};

callbackTest("Hey", isAString => isAString);

answered May 20, 2022 at 16:03

k.tten

26.8k4 gold badges34 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

typescript callback with generic function

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related