callback vs dfd

dfd-foo.js

// old way, plan to pass a func
function doAsyncStuff(callback){
  
  // do stuff, then call the function that was passed
  setTimeout(callback,2000);
}

// calling it
doAsyncStuff(function(){
  console.log('internet website')
})

/////////////////////////

// new way
// assumes Q.js has been loaded and available as Q (could also use jQuery)
function doMoreAsync(){
  var dfd = Q.defer();
  
  // in 2000 secs, *resolve* promise with data
  setTimeout(function(){
    dfd.resolve({foo: 'bar'})
    
    // or reject for whatever reason
    // dfd.reject({error: 'fail'})
    
  },2000)

  // return promise
  return dfd.promise
}

/* async func returns a promise object. Promises have a method named 'then' */
doMoreAsync()
  .then(function(data){
    // do stuff with the data
    console.log('the promise was resolved', data)
  }).fail(function(error){
    // handle rejected promise
    console.log('promise rejected, error callback', error)
  })