typescript class mixins

event-emittable.ts

import { Mixin } from './mixin';
import { EventEmitter } from 'events';

// Define .h
export declare class EventEmittable {
  protected events: EventEmitter;
}

// Implement .cpp
export const EventEmittableMixin = (mixin: Mixin) => class extends mixin {
  protected events: EventEmitter;
  constructor() {
    super();
    this.events = new EventEmitter();
  }
};

example.ts

import { mixin } from './mixin';
import { EventEmittable, EventEmittableMixin } from './event-emittable';

/**
* Just like in C language:
* 1. Define .h
* 2. Implement .cpp
* 3. Use
*/

// Define
export declare interface MyClass extends EventEmittable { };

// Implement
export class MyClass extends mixin(EventEmittableMixin) {
  constructor() {
    super();
  }
}

mixin.ts

declare class Base { };

export type Mixin = typeof Base;

function Mixin(BaseClass: Mixin = class { }) {
  return (...Mixins: Array<(Base: Mixin) => Mixin>) => {
    return Mixins.reduce((c, mixin) => mixin(c), BaseClass);
  };
}

export const mixin = Mixin();

This example assumes that you prefer agregation to inheritance in most cases, so that we can always have an option to share code across files.