TypeScript Functions Function as a parameter


Example

Suppose we want to receive a function as a parameter, we can do it like this:

function foo(otherFunc: Function): void {
    ...
}

If we want to receive a constructor as a parameter:

function foo(constructorFunc: { new() }) {
    new constructorFunc();
}

function foo(constructorWithParamsFunc: { new(num: number) }) {
    new constructorWithParamsFunc(1);
}

Or to make it easier to read we can define an interface describing the constructor:

interface IConstructor {
    new();
}

function foo(contructorFunc: IConstructor) { 
    new constructorFunc();
}

Or with parameters:

interface INumberConstructor {
    new(num: number);
}

function foo(contructorFunc: INumberConstructor) {
    new contructorFunc(1);
}

Even with generics:

interface ITConstructor<T, U> {
    new(item: T): U;
}

function foo<T, U>(contructorFunc: ITConstructor<T, U>, item: T): U {
    return new contructorFunc(item);
}

If we want to receive a simple function and not a constructor it's almost the same:

function foo(func: { (): void }) {
    func();
}

function foo(constructorWithParamsFunc: { (num: number): void }) {
    new constructorWithParamsFunc(1);
}

Or to make it easier to read we can define an interface describing the function:

interface IFunction {
    (): void;
}

function foo(func: IFunction ) { 
    func();
}

Or with parameters:

interface INumberFunction {
    (num: number): string;
}

function foo(func: INumberFunction ) {
    func(1);
}

Even with generics:

interface ITFunc<T, U> {
    (item: T): U;
}

function foo<T, U>(contructorFunc: ITFunc<T, U>, item: T): U {
    return func(item);
}