callback-hell.js

// An approach based upon event emitters                                                                                                          
const EventEmitter = require('events')                                                                                                            
                                                                                                                                                  
const getLargeExternalDataEvent = (url) => {                                                                                                      
  setTimeout(() => {                                                                                                                              
    console.log('fetching data from ' + url + '...')                                                                                              
    q.emit('data', genLongString(url))                                                                                                            
  } , 1000)                                                                                                                                       
}                                                                                                                                                 
                                                                                                                                                  
const getSizeEvent = (data) => {                                                                                                                  
  setTimeout(() => {                                                                                                                              
    console.log('calculating size of data...')                                                                                                    
    q.emit('size', data.length)                                                                                                                   
  }, 1000)                                                                                                                                        
}                                                                                                                                                 
                                                                                                                                                  
const intoMBsEvent = (size) => {                                                                                                                  
  setTimeout(() => {                                                                                                                              
    q.emit('mbs', (size / 1024))                                                                                                                  
  }, 1000)                                                                                                                                        
}                                                                                                                                                 
                                                                                                                                                  
const q = new EventEmitter()                                                                                                                      
                                                                                                                                                  
q.on('data', (data) => getSizeEvent(data))                                                                                                        
q.on('size', (size) => intoMBsEvent(size))                                                                                                        
q.on('mbs', (mbs) => postResult(mbs))                                                                                                             
                                                                                                                                                  
getLargeExternalDataEvent('wat.event')