interface GameEvent {
    gameStarted(name: string): void
}

class Game {
    public name: string
    private _listeners: GameEvent[]

    constructor(name: string) {
        this.name = name;
        this._listeners = [];
    }

    addListener(listener: GameEvent) {
        this._listeners.push(listener);
    }

    start() {
        for (let listener of this._listeners) {
            listener.gameStarted(this.name);
        }
    }
}

class Statistic implements GameEvent {

    public startsCount: number = 0
    public lastGame: string = ""

    gameStarted(name: string) {
        this.startsCount++;
        this.lastGame = name;
    }
}

let statistic = new Statistic()
let heroes = new Game("Heroes")
let doom = new Game("Doom")

//subscribe to events
heroes.addListener(statistic)
doom.addListener(statistic)

doom.start()
heroes.start()
//statistic.lastGame is "Heroes"
//statistic.startsCount is 2

console.log("lastGame is", 
    statistic.lastGame)
console.log("startsCount is", 
    statistic.startsCount)