Provide an interface for NodeJs EventEmitter with event name and event argument type checking.

Install

npm i eei.ts

Usage

import { EventEmitter } from "events"; // import EventEmitter from `@type/node`.
import EEI from "eei.ts"; // import EEI interface.

// define events
interface PlayerEvents {
    damaged: [Player, number];
    death: [Player];
}

class Player {
    // Store private EventEmitter with full interface.
    private readonly _events = new EventEmitter() as EEI<PlayerEvents>;
    // private readonly _events: EEI<PlayerEvents> = new EventEmitter(); // is not working : EventEmitter must be cast with `as` keyword.
    private _hp: number;

    constructor(public readonly name: string, public readonly maxHp: number) {
        this._hp = maxHp;
    }

    // Expose the EventEmitter with limited interface. (subscribe and unsubscribe methods only).
    get events() {
        return this._events as EEI<PlayerEvents, "_subscription">;
    }

    get hp() {
        return this._hp;
    }

    dealDamage(amount: number) {
        this._hp = this._hp < amount ? 0 : this._hp - amount;
        this._events.emit("damaged", this, amount);
        if (this._hp <= 0) this._events.emit("death", this);
    }
}

const bob = new Player("Bob", 100);
bob.events
    .on("damaged", (player, amount) => {
        console.log(
            `${player.name} took ${amount} damage. [${player.hp}/${player.maxHp}]`
        );
    })
    .once("death", (player) => {
        console.log(`${player.name} is dead.`);
        player.events.removeAllListeners();
    });

bob.dealDamage(40);
bob.dealDamage(70);
bob.dealDamage(10);

API

The interface

The interface take two generic type:

• the event definition
• the EventEmitter methods or presset

examples

type EventEmitterWithAllMethods = EEI<MyEvents>;
type EventEmitterWithSubscriptionMethods = EEI<MyEvents, "on" | "once" | "off">;
type EventEmitterWithSubscriptionMethodsWithPresset = EEI<MyEvents, "_subscription">;

Presset

All presset start with _.

• _subscribe = "on" | "once" | "addListener" | "prependListener" | "prependOnceListener"
• _unsubscribe = "off" | "removeListener" | "removeAllListeners"
• _subscription = "_subscribe" | "_unsubscribe"

Define events

Create an interface:

• key: event name, must be a string or a symbol.
• type: a tuple with event's argument types

interface MyEvents {
   eventName: [string, number];
   anotherEvent: [];
}

Author

👤 Tristan Guichaoua

• Website: tguichaoua.github.io
• Github: @tguichaoua

🤝 Contributing

Contributions, issues and feature requests are welcome!Feel free to check issues page. You can also take a look at the contributing guide.

Show your support

Give a ⭐️ if this project helped you!

📝 License

Copyright © 2020 Tristan Guichaoua. This project is MIT licensed.

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