Does the $http promise consistently deliver the initial promise?

Forgive me if this question isn't up to par, but it's been causing some confusion.

I've been trying to extract specific data from an $http.post() method within a factory. However, it seems like $http always returns the initial promise. I want to avoid using .success and .error due to their potential deprecation in v1.5. Additionally, since the factory may perform other tasks such as saving items in localStorage, I don't want to directly return $http.post().

So, is the following code snippet the most efficient way to retrieve specific data from an angular $http promise?

function login (email, password) {
  var deferred = $q.defer();

  $http.post('/api/auth', {
    email: email,
    password: password
  })
    .then(function (data) {
      return deferred.resolve('success');
    })
    .catch(function (data) {
      return deferred.reject('fail');
    });

  return deferred.promise;
}

Answer №1

Forget about creating a deferred object. Just return the result directly from $http.post. This method returns a promise with additional methods (success and failure).

function login(email, password) {
  return $http.post('/api/auth', {
    email: email,
    password: password
  })
  .then(function (data) {
    var newData = translateData(data);
    //passing data to the next promise
    return newData;
  })
  .catch(function (reason) {
    /*handle failure*/
    //rejection reason propagated to the next promise
    return $q.reject(reason);
  });
}

login()
  //Access your data here.
  .then(function (data) { console.log(data); }) 
  .catch(function (reason) { console.log(reason); });

Check out this blog post for insights on how to handle data propagation and rejection reasons in promise chains.

Answer №2

To handle errors in the 'then' method, I suggest placing the error response as the second callback (as shown below). This ensures that the error callback will only be executed if there is an issue with the $http request.

function authenticate(email, password) { 
   var deferred = $q.defer();
   $http.post('/api/auth', {
     email: email,
     password: password
   })
   .then(function(data) {
     return deferred.resolve(data);
   }, function(message) {
     return deferred.reject(message);
   });
   return deferred.promise;
}

Your current approach using catch() means it will be triggered for any error in a promise chain. It is typically used at the end of multiple promises, like this:

CustomerService.authenticate(email, password)
   .then(getUserData)
   .then(setUpAccount)
   .catch($log.error);

For more detailed information on promises, you can refer to this informative post: Promises and Design Patterns in AngularJS

Additionally, explore the documentation on promises, specifically the section on 'The Promise API'

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