JavaScript Callbacks vs Promises

callback-vs-promises.js

// *******************
// callback version
// *******************

function getDataCallback(data) {
  // do something with the new data data
}

function getData(callback) {
  // getting the data
  // send the data through the callback
  callback(data)
}

getData(getDataCallback);



// *******************************
// Promise example using mongoose
// *******************************

//save a new book to the database
newBook.save()
  .then(() => {
  // query the database for all of the books
  return Books.find({});
  })
  .then(books => {
    //do something with all the books
  })
  .catch(err => {
    console.error(err);
  })

// ***********************************
// NOT recommended way to use promises
// ************************************
// This is trying to use promises like you use callbacks and defeats the purpose of promises, still putting you in 'callback hell'
// Also not DRY
newBook.save()
  .then(() => {
    Books.find({})
      .then(books => {
        // do something with the books.
      })
      .catch(err => {
        console.error(err);
      })
  }).catch(err => {
    console.error(err);
  })