How can you define a type for onSubmit in a Typescript interface?

Question

Within my React app I have an interface in which I also specify the onSubmit method optionally and with the any type (which I want to avoid). So I'm looking for a way to define a type for the onSubmit method.

This is my interface:

export interface CustomInterface {
  product?: ProductClass;
  loggedInUser: UserClass;
  headerTitle?: (s: string) => any;
  onSubmit?: any; // Here I need a better type
}

How can I optimize this interface?

Answer 1

Try this:

export interface CustomInterface {
  product?: ProductClass;
  loggedInUser: UserClass;
  headerTitle?: (s: string) => any;
  onSubmit?: (data:Define your type here like string,boolean and so on)=>void // Here I need a better type
}

Answer 2

I would suggest to do something like this:

export interface CustomInterface {
  product?: ProductClass;
  loggedInUser: UserClass;
  headerTitle?: (s: string) => any;
  onSubmit?(): void;
}

Or lets say onSubmit function needs an string param:

export interface CustomInterface {
  product?: ProductClass;
  loggedInUser: UserClass;
  headerTitle?: (s: string) => any;
  onSubmit?(s: string): void;
}

This you declare onSubmit has type function.