Observable

observable.js

class Observable {
  constructor() {
    this._handlers = []
  }
  
  subscribe(event, handler) {
    this._handlers[event] = this._handlers[event] || []
    this._handlers[event].push(handler)
  }
  
  publish(event, eventData) {
    const eventHandlers = this._handlers[event]
    
    if (eventHandlers) {
      for (var i = 0, l = eventHandlers.length; i < l; ++i) {
        eventHandlers[i].call({}, eventData)
      }
    }
  }
}

Hi Jordan,
I'm having a hard time in understanding 7th line. Could u please help me in understanding what's the purpose of this line?

Hi Jordan,
I'm having a hard time in understanding 7th line. Could u please help me in understanding what's the purpose of this line?

It either takes the currently created event array if it is presented in this._handlers and if not it creates a new empty event array

const handlers = [];                           // OUTPUT: []
handlers['event1'] = handlers['event1'] || []; // OUTPUT: [event1: []]
handlers['event2'] = handlers['event2'] || []; // OUTPUT: [event1: [], event2: []]

handlers['event1'] = handlers['event1'] || []; // OUTPUT: [event1: [], event2: []]

handlers['event1'].push('user1');              // OUTPUT: [event1: ['user1'], event2: []]
handlers['event1'] = handlers['event1'] || []; // OUTPUT: [event1: ['user1'], event2: []]