Method addHandler

src/utils/Event.ts:23–26

(cb: Callback<EventType>)

    }

    public addHandler(cb: Callback<EventType>): () => void {
        this._callbacks.push(cb);
        return () => this.removeHandler(cb);
    }

    public removeHandler(cb: Callback<EventType>): void {
        const idx = this._callbacks.lastIndexOf(cb);