promises-vs-callbacks.js

// callbacks

foo(params, function (error, fooResult) {
  bar(fooResult, function (error, barResult) {
     baz(barResult, function (error, bazResult) {
       // and on and on... >>>>>>>
     });
  });
});

// vs.

// promises

foo(params)
  .then(bar)
  .then(baz)
  .catch(handleError);

function handleError(error) {
  // ...
};