binier / tiny-typed-emitter

Fully type-checked NodeJS EventEmitter

tiny-typed-emitter

Have your events and their listeners type-checked with no overhead.

Install

Simply add the dependency using npm:

$ npm i tiny-typed-emitter

or using yarn:

$ yarn add tiny-typed-emitter

Usage

1. import tiny-typed-emitter library:

import { TypedEmitter } from 'tiny-typed-emitter';

2. define events and their listener signatures (note: quotes around event names are not mandatory):

interface MyClassEvents {
  'added': (el: string, wasNew: boolean) => void;
  'deleted': (deletedCount: number) => void;
}

3. on this step depending on your use case, you can:

• define your custom class extending EventEmitter:

  class MyClass extends TypedEmitter<MyClassEvents> {
    constructor() {
      super();
    }
  }

• create new event emitter instance:

  const emitter = new TypedEmitter<MyClassEvent>();

Generic events interface

To use with generic events interface:

interface MyClassEvents<T> {
  'added': (el: T, wasNew: boolean) => void;
}

class MyClass<T> extends TypedEmitter<MyClassEvents<T>> {

}

Compatible subclasses with different events

The type of eventNames() is a superset of the actual event names to make subclasses of a TypedEmitter that introduce different events type compatible. For example the following is possible:

class Animal<E extends ListenerSignature<E>=ListenerSignature<unknown>> extends TypedEmitter<{spawn: () => void} & E> {
  constructor() {
    super();
  }
}

class Frog<E extends ListenerSignature<E>> extends Animal<{jump: () => void} & E> {
}

class Bird<E extends ListenerSignature<E>> extends Animal<{fly: () => void} & E> {
}

const animals: Animal[] = [new Frog(), new Bird()];

No Overhead

Library adds no overhead. All it does is it simply reexports renamed EventEmitter with customized typings. You can check lib/index.js to see the exported code.

tiny-typed-emitter's Issues

[Question] Trying to expose specific methods only

Hi, I am trying to expose only the following methods to an API:

• on, once, off

I want to emit stuff internally and expose only those 3 methods.

Here what I got as of now:

interface SocketEvents {
    'socket-connected': () => void
    'socket-disconnected': () => void
    'socket-reply': (event: string, ...params: any[]) => void
    'socket-error': (event: string, error: any) => void
}
class SocketEventEmitter extends TypedEmitter<SocketEvents> {
    constructor() { super() }
}
const eventEmitter = new SocketEventEmitter()

export function on(event: keyof SocketEvents, listener: SocketEvents[keyof SocketEvents]) {
    eventEmitter.on(event, listener)
}
export function once(event: keyof SocketEvents, listener: SocketEvents[keyof SocketEvents]) {
    eventEmitter.once(event, listener)
}
export function off(event: keyof SocketEvents, listener: SocketEvents[keyof SocketEvents]) {
    eventEmitter.off(event, listener)
}

The problem I'm facing with this, is the exported on, once, off doesn't automatically detect the correct listener to use.
I believe it might just be something to do with listener: SocketEvents[keyof SocketEvents].

I was wondering if anyone would have a solution for this.

Edit:
I tried this also

export const on = eventEmitter.on
export const once = eventEmitter.once
export const off = eventEmitter.off

But the return of the call expose the whole object

Keep default any event type

In my use case I am extending a library which has some static event names and some are dynamic generated.
So I would like to have some events typed but keep the default any emitter.
I adapted your library for this and wanted the share the code.
I think this is a general use case and would fit in this library.
So if you like it you could export it as an additional interface something like LooselyTypedEmitter<L>.
Note that this will prevent strict type checking, so it is not a replacement.

declare type DefaultFunction = (...args: any[]) => any;
declare type ListenerSignature<L> = {
    [E in keyof L]: DefaultFunction;
};

declare type DefaultListener = {
    [k: string]: DefaultFunction;
};

export class LooselyTypedEmitter<L extends ListenerSignature<L> = DefaultListener> {
    static defaultMaxListeners: number;
    addListener<U extends keyof L>(event: U, listener: L[U]): this;
    addListener(event: string, listener: DefaultFunction): this;
    prependListener<U extends keyof L>(event: U, listener: L[U]): this;
    prependListener(event: string, listener: DefaultFunction): this;
    prependOnceListener<U extends keyof L>(event: U, listener: L[U]): this;
    prependOnceListener(event: string, listener: DefaultFunction): this;
    removeListener<U extends keyof L>(event: U, listener: L[U]): this;
    removeListener(event: string, listener: DefaultFunction): this;
    removeAllListeners(event?: keyof L): this;
    removeAllListeners(event?: string): this;
    once<U extends keyof L>(event: U, listener: L[U]): this;
    once(event: string, listener: DefaultFunction): this;
    on<U extends keyof L>(event: U, listener: L[U]): this;
    on(event: string, listener: DefaultFunction): this;
    off<U extends keyof L>(event: U, listener: L[U]): this;
    off(event: string, listener: DefaultFunction): this;
    emit<U extends keyof L>(event: U, ...args: Parameters<L[U]>): boolean;
    emit(event: string, ...args: any[]): boolean;
    eventNames<U extends keyof L>(): U[];
    listenerCount(type: keyof L): number;
    listenerCount(type: string): number;
    listeners<U extends keyof L>(type: U): L[U][];
    listeners(type: string): DefaultFunction[];
    rawListeners<U extends keyof L>(type: U): L[U][];
    rawListeners(type: string): DefaultFunction[];
    getMaxListeners(): number;
    setMaxListeners(n: number): this;
}

How would I specify a function as one of the items emitted

i.e.

interface Events { 'message': (message: any, done: function) => void }

Provide also raw interface definition instead of just class

First, thanks for this helpful package @binier ! I used to manually declare onX(…) events to enforce typed events until I found it.

One thing I miss is a plain interface definition which I can inherit.

export interface ITypedEmitter<L extends ListenerSignature<L> = DefaultListener> {
    addListener<U extends keyof L>( event: U, listener: L[U] ): this;
    prependListener<U extends keyof L>( event: U, listener: L[U] ): this;
    // etc.
}

export interface MyInterfaceWithEvents extends ITypedEmitter<MyEvents> {
    // …
}

so users of the interface can also rely on typed events, not only users of the instance.

Can we use the emit method with a variable for the event name instead of string?

When emitting, can we use a variable instead of a string?

like this:
this.emit(some_variable, args)

Cannot find module 'tiny-typed-emitter' or its corresponding type declarations.ts(2307)

ButtonBehavior.ts:

import { ButtonBehaviorEvent } from './ButtonBehaviorEvent'
import { TypedEmitter } from 'tiny-typed-emitter';

export class ButtonBehavior extends TypedEmitter<ButtonBehaviorEvent> {

  constructor() {
    super();
    this.emit('buttonBehaviorEvent', 'over', true, true, false);
  }

}

ButtonBehaviorEvent.ts:

export interface ButtonBehaviorEvent {
  
  'buttonBehaviorEvent': (
                            $state: string, 
                            $selected: boolean, 
                            $enabled: boolean, 
                            $pressed: boolean,
                          ) => void;
}

package.json:

{
  "name": "drawing",
  "version": "1.0.0",
  "scripts": {
    "dev": "webpack --mode development",
  },
  "devDependencies": {
    "@types/fabric": "^3.6.8",
    "@types/jquery": "^3.5.1",
    "@types/node": "^14.6.4",
    "css-loader": "^4.2.2",
    "mini-css-extract-plugin": "^0.11.0",
    "sass": "^1.26.10",
    "sass-loader": "^10.0.2",
    "ts-loader": "^8.0.3",
    "typescript": "^4.0.2",
    "webpack": "^4.44.1",
    "webpack-cli": "^3.3.12"
  },
  "dependencies": {
    "tiny-typed-emitter": "^2.0.2"
  }
}

I get the errors:

From VScode:
Cannot find module 'tiny-typed-emitter' or its corresponding type declarations.ts(2307)

After compilation:
ButtonBehavior.ts - TS2315: Type 'EventEmitter' is not generic.
ButtonBehavior.ts - TS2339: Property 'emit' does not exist on type 'ButtonBehavior'.

Issue with subclasses

Hi, thanks for the great library 👍

I have a question about the subclasses with different events example that you provided in the readme:

The example works when calling the events from outside the class, but not from within the class itself. Specifically, if I alter the example to be as follows:

class Animal<E extends ListenerSignature<E> = ListenerSignature<unknown>> extends TypedEmitter<{ spawn: () => void } & E> {
	public constructor() {
		super();
	}

	private doSpawn() {
		this.emit('spawn');
	}
}

class Frog<E extends ListenerSignature<E>> extends Animal<{ jump: (testing: boolean) => void } & E> {}
class Bird<E extends ListenerSignature<E>> extends Animal<{ fly: () => void } & E> {}

Then the compiler fails at the this.emit('spawn'); line with the error: Argument of type '[]' is not assignable to parameter of type 'Parameters<({ spawn: () => void; } & E)["spawn"]>'.

I'm assuming this is because of some constraint that can't be applied, but I can't seem to wrap my head around it. Is there any way to solve this?

adding typed events to an extended class that extends EventEmitter?

hi, i'm creating a class that extends the Stream class, which extends EventEmitter. does this module support adding typed events to such classes?

interface MyEvents {
  'foo': () => void;
}

// how do I fit `TypedEmitter` here so that `MyClass` has the `foo` event and also extends `Stream`?
class MyClass extends Stream {
  constructor() {
  }
}