books/utils/observable.js

module.exports = class Observable {
	constructor() {
		this._handlers = {};
	}

    on(event, fn) {
        if (!this._handlers[event]) {
			this._handlers[event] = [];
		}
        this._handlers[event].push(fn);
    }

    async trigger(event, params) {
        if (this._handlers[event]) {
            for (let handler of this._handlers[event]) {
                await handler(params);
            }
        }
    }
}