Observer Pattern pt1

eventemitter.js

// implementing event emitter pattern 
class EventEmitter {
  constructor() {
    this.events = {} // initialize with empty events object
  }

  addEventListener(eventLabel, callback) {  // create a new key for our event with the eventLabel
    if (!this.events[eventLabel])
      this.events[eventLabel] = []
    
    this.events[eventLabel].push(callback)
  }

  dispatchEvent(eventLabel, data) {
    const event = this.events[eventLabel] // lookup the event in events object
    if (event) {
      event.forEach(callback => { // iterate through each function assigned to the event label
        callback.call(null, data) // call the function with null as the 'thisArg', and the data passed in
      })
    }
  }
}