Class constructor type in typescript?

Question

How can I declare a class type, so that I ensure the object is a constructor of a general class?

In the following example, I want to know which type should I give to AnimalClass so that it could either be Penguin or Lion:

class Animal {
    constructor() {
        console.log("Animal");
    }
}

class Penguin extends Animal {
    constructor() {
        super();
        console.log("Penguin");
    }
}

class Lion extends Animal {
    constructor() {
        super();
        console.log("Lion");
    }
}

class Zoo {
    AnimalClass: class // AnimalClass could be 'Lion' or 'Penguin'

    constructor(AnimalClass: class) {
        this.AnimalClass = AnimalClass
        let Hector = new AnimalClass();
    }
}

Of course, the class type does not work, and it would be too general anyway.

Answer 1

Like that:

class Zoo {
    AnimalClass: typeof Animal;

    constructor(AnimalClass: typeof Animal ) {
        this.AnimalClass = AnimalClass
        let Hector = new AnimalClass();
    }
}

Or just:

class Zoo {
    constructor(public AnimalClass: typeof Animal ) {
    }
}

typeof Class is the type of the class constructor. It's preferable to the custom constructor type declaration because it processes static class members properly.

Answer 2

Solution from typescript interfaces reference:

interface ClockConstructor {
    new (hour: number, minute: number): ClockInterface;
}
interface ClockInterface {
    tick();
}

function createClock(ctor: ClockConstructor, hour: number, minute: number): ClockInterface {
    return new ctor(hour, minute);
}

class DigitalClock implements ClockInterface {
    constructor(h: number, m: number) { }
    tick() {
        console.log("beep beep");
    }
}
class AnalogClock implements ClockInterface {
    constructor(h: number, m: number) { }
    tick() {
        console.log("tick tock");
    }
}

let digital = createClock(DigitalClock, 12, 17);
let analog = createClock(AnalogClock, 7, 32);

So the previous example becomes:

interface AnimalConstructor {
    new (): Animal;
}

class Animal {
    constructor() {
        console.log("Animal");
    }
}

class Penguin extends Animal {
    constructor() {
        super();
        console.log("Penguin");
    }
}

class Lion extends Animal {
    constructor() {
        super();
        console.log("Lion");
    }
}

class Zoo {
    AnimalClass: AnimalConstructor // AnimalClass can be 'Lion' or 'Penguin'

    constructor(AnimalClass: AnimalConstructor) {
        this.AnimalClass = AnimalClass
        let Hector = new AnimalClass();
    }
}