.js

//these two scripts are equivalent
somePromise().catch(function (err) {
  // handle error
});

somePromise().then(null, function (err) {
  // handle error
});


//these two scripts are not equivalent
somePromise().then(function () {
  return someOtherPromise();
}).catch(function (err) {
  // handle error
});

somePromise().then(function () {
  return someOtherPromise();
}, function (err) {
  // handle error
});