Mixins for TypeScript

mixin.ts

export interface Empty {}

export interface Class<T> {
  new(): T;
}

export type Super = Class<Empty>;

export interface Mixin<M, S> {
  <T extends S>(s: Class<T>): Class<T & M>;
}

export function mixin<M>() {
  return function<S>(fn: (s: Class<S>) => Class<S & M>): Mixin<M,S> {
    return fn;
  }
}

export default mixin;

mixin_example.ts

import {mixin, Class, Super} from './mixin';

export class A {
  a() {
    return 1;
  }
}

export interface B {
  b(): number;
}

const B = mixin<B>()((s: typeof A) => class extends s implements B {
  a() {
    return super.a();
  }
  b() {
    console.log(this.a());
    return 2;
  }
})

export interface C {
  c(): number;
}

const C = mixin<C>()((s: Super) => class extends s implements C {
  c() {
    return 3;
  }
})

export interface ABC extends A,B,C {};

// Has proper superclass verification.
export const ABC: Class<ABC> = C(B(A));
export class D extends ABC {
  foo() {
    console.log(this.a(), this.b(), this.c());
  }
}