Typed NodeJS.EventEmitter

README.md

const emitter: TypedEventEmitter<{
  start: () => void;
  stop: () => void;
  progress: (progress: number) => void;
}> = new EventEmitter();

emitter.on('progress', (progress) => {
  // foo
});

export interface IRecorder extends TypedEventEmitter<{
  start: () => void;
  stop: () => void;
  progress: (progress: number) => void;
}> {
  start(): Promise<void>;
  stop(): Promise<void>;
}

class Recorder extends EventEmitter implements IRecorder {
  // ...
}

const rec: IRecorder = new Recorder();
rec.on('progress', (progress) => {
  // ...
});

TypedEventEmitter.ts

import EventEmitter from 'events';

export default interface TypedEventEmitter<Emits extends TypedEmits> extends EventEmitter {
  addListener<K extends keyof Emits>(event: K, listener: Emits[K]): this;
  emit<K extends keyof Emits>(event: K, ...args: Parameters<Emits[K]>): boolean;
  off<T extends keyof Emits>(type: T, listener: Emits[T]): this;
  on<T extends keyof Emits>(type: T, listener: Emits[T]): this;
  once<T extends keyof Emits>(type: T, listener: Emits[T]): this;
  prependListener<T extends keyof Emits>(type: T, listener: Emits[T]): this;
  prependOnceListener<T extends keyof Emits>(type: T, listener: Emits[T]): this;
  removeAllListeners<T extends keyof Emits>(type?: T): this;
  removeListener<T extends keyof Emits>(type: T, listener: Emits[T]): this;
}

type EmitParameters = Parameters<typeof EventEmitter.prototype.emit>;
type TypedEmits = Record<EmitParameters[0], EmitParameters[1]>;