event emitters example

emitters.js

const {EventEmitter} = require('events')

// initialization
const ee = new EventEmitter()
ee.isReady = false
ee.on('ready', function() {ee.isReady = true})
ee.onReady = function(cb) {
  if (this.isReady) {
    // call immediately
    cb()
  } else {
    // attach a handler
    this.once('ready', cb)
  }
}

// ... some time passes
// has ready been emitted? then trigger immediately! otherwise wait for it
ee.onReady(() => console.log('ready!'))

// in the future
ee.emit('ready')

// should also be called
ee.onReady(() => console.log('still ready?'))