subscribe(event, callback) {
        
        let self = this;
        
        // If there's not already an event with this name set in our collection
        // go ahead and create a new one and set it with an empty array, so we don't
        // have to type check it later down-the-line
        if(!self.events.hasOwnProperty(event)) {
            self.events[event] = [];
        }
        
        // We know we've got an array for this event, so push our callback in there with no fuss
        return self.events[event].push(callback);
    }
/**
     * Either create a new event instance for passed `event` name
     * or push a new callback into the existing collection
     *
     * @param {string} event
     * @param {function} callback
     * @returns {number} A count of callbacks for this event
     * @memberof PubSub
     */
Either create a new event instance for passed `event` name
or push a new callback into the existing collection

@param {string} event
@param {function} callback
@returns {number} A count of callbacks for this event
@memberof PubSub
Either create a new event instance for passed ` event ` name or push a new callback into the existing collection @param { string } event @param { function } callback @returns { number } A count of callbacks for this event @memberof PubSub
subscribe(event, callback) {
        let self = this;
        if(!self.events.hasOwnProperty(event)) {
            self.events[event] = [];
        }
        return self.events[event].push(callback);
    }
subscribe ( event , callback ) { let self = this ; if ( ! self . events . hasOwnProperty ( event ) ) { self . events [ event ] = [ ] ; } return self . events [ event ] . push ( callback ) ; }
Either create a new event instance for passed `event` name
 or push a new callback into the existing collection
Either create a new event instance for passed ` event ` name or push a new callback into the existing collection
// If there's not already an event with this name set in our collection // go ahead and create a new one and set it with an empty array, so we don't // have to type check it later down-the-line // We know we've got an array for this event, so push our callback in there with no fuss