Is there a type for callback functions in TypeScript?

Question

enter image description here The error says Supplied parameter do not match any signature of call target. When I replace Function with any as the second parameter's type, the error disappears. But any is the same as no type, isn't there a suitable type for functions as parameters?

Fenton · Accepted Answer · 2015-02-05 13:53:41Z

12

Instead of Function (or any) you can use the following type for your callback parameter:

(ev: Event)=> any

This matches the type expected by addEventListener.

Here is the full function signature:

on(eventName: string, callback: (ev: Event)=> any, useCapture: boolean) : Dom.Element {
    //...

answered Feb 5, 2015 at 13:53

Fenton

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2 Comments

jstice4all Over a year ago

Ok. So it means the type is function with ev parameter of type Event that returns any?

Fenton Over a year ago

Yes - although think of the return type as simply being very permissive. You can pass a function that returns void, or a string, or a number - whatever you like; allow any return type.

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