Generic and typeof T in the parameters

Question

In TypeScript I can define the type of a variable as the type of a class. For example:

class MyClass { ... }

let myVar: typeof MyClass = MyClass;


        

Answer 1

You can use this type of constructors: { new (): ClassType }.

class MyManager<T> {
    private cls: { new(): T };

    constructor(cls: { new(): T }) {
        this.cls = cls;
    }

    createInstance(): T {
        return new this.cls();
    }
}

class MyClass {}

let test = new MyManager(MyClass);
let a = test.createInstance();
console.log(a instanceof MyClass); // true

(code in playground)

---

Edit

The proper way to describe a class type in typescript is using the following:

{ new(): Class }

For example in the typescript lib.d.ts ArrayConstructor:

interface ArrayConstructor {
    new (arrayLength?: number): any[];
    new <T>(arrayLength: number): T[];
    new <T>(...items: T[]): T[];
    (arrayLength?: number): any[];
    <T>(arrayLength: number): T[];
    <T>(...items: T[]): T[];
    isArray(arg: any): arg is Array<any>;
    readonly prototype: Array<any>;
}

Here you have 3 different ctor signatures plus a bunch of static functions.
In your case you can also define it like:

interface ClassConstructor<T> {
    new(): T;
}

class MyManager<T> {
    private cls: ClassConstructor<T>;

    constructor(cls: ClassConstructor<T>) {
        this.cls = cls;
    }

    createInstance(): T {
        return new this.cls();
    }
}

Answer 2

You can just declare it by the following type.

variableName: typeof ClassName;

typeof is Javascript keyword.