TypeScript: Type of a class

Question

I simply want to create a function that takes a class as argument:

const mixin = (traits: Object) =>
  (baseClass: class) => { // What type to put here?
    Object.assign(baseClass.prototype, traits)
    return baseClass
  }

But I don't know what type I have to put to specify I'm working with a Constructor Function.

Nitzan Tomer · Accepted Answer · 2016-10-31 23:15:42Z

4

You can use generics to return the right class constructor:

const mixin = (traits: any) =>
    <T>(baseClass: { new (): T }) => {
        Object.assign(baseClass.prototype, traits);
        return baseClass;
    }

class A {}

let o = mixin({})(A); // typeof o is new () => A
let a = new o(); // typeof a is A

(code in playground)

answered Oct 31, 2016 at 23:15

Nitzan Tomer

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2 Comments

kube Over a year ago

Thanks, that works. But I'm still facing some issues : mixin(Speaker)(class { }) works, but mixin(Speaker)(class extends Mammal { }) does not. Am I missing something?

kube Over a year ago

Sorry, was doing something bad. Works perfectly. Thanks.

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