How do I instantiate a javascript object from class reference?

Question

I want to be able to instantiate objects in javascript (typescript) from a reference to the class. For instance, I want to be able to use some kind of factory function like so, but I don't know how to achieve this result.

class A {
    constructor() { this.b = 'somevalue'; }
}

const factory = (klass: Function) => {
    return new klass();
}

const instanceOfA = factory(A);

This example is rather contrived, but is there a way of doing this? The current error says klass is not a constructor. Alternatively if there's a more idiomatic way of instantiating things from a class reference, I'd love to hear it. Thanks!

Answer 1

Function is just the wrong type, use a constructor type (which also helps infering the correct return type):

function factory<T>(klass: { new(): T }): T {
   return new klass();
}

Or as a const you assign to:

const factory = <T>(klass: { new(): T }) => {
    return new klass();
};