Typescript: How to define type for a function callback (as any function type, not universal any) used in a method parameter

Question

Currently I have type definition as:

interface Param {
    title: string;
    callback: any;
}

I need something like:

inter         


        

Answer 1

There are four abstract function types, you can use them separately when you know your function will take an argument(s) or not, will return a data or not.

export declare type fEmptyVoid = () => void;
export declare type fEmptyReturn = () => any;
export declare type fArgVoid = (...args: any[]) => void;
export declare type fArgReturn = (...args: any[]) => any;

like this:

public isValid: fEmptyReturn = (): boolean => true;
public setStatus: fArgVoid = (status: boolean): void => this.status = status;

For use only one type as any function type we can combine all abstract types together, like this:

export declare type fFunction = fEmptyVoid | fEmptyReturn | fArgVoid | fArgReturn;

then use it like:

public isValid: fFunction = (): boolean => true;
public setStatus: fFunction = (status: boolean): void => this.status = status;

In the example above everything is correct. But the usage example in bellow is not correct from the point of view of most code editors.

// you can call this function with any type of function as argument
public callArgument(callback: fFunction) {

    // but you will get editor error if call callback argument like this
    callback();
}

Correct call for editors is like this:

public callArgument(callback: fFunction) {

    // pay attention in this part, for fix editor(s) error
    (callback as fFunction)();
}