Why are AngularJS $http success/error methods deprecated? Removed from v1.6?

The problem was that .success and .error methods are not chainable because they ignore return values. This caused problems for people familiar with chaining and encouraged poor code from people unfamiliar with chaining. Witness all the examples on StackOverflow that use the deferred anti-pattern.

To quote one of the AngularJS team:

IMO .success and .error were a bad bit of API design in the first place. This issue highlights a number of situations where developers get confused because they either expect .success and .error to work the same way as .then or vice versa. In a perfect world I would rather just ditch these $http specific "promises". Instead we could encourage developers to use the standard $q promise API .then and .catch. There is very little benefit IMO in working with explicit parameters over working with the response object.

— AngularJS Issue #10508 $http .success/.error dissimilar from how .then works.

Deprecation Notice (v1.5)

The $http legacy promise methods success and error have been deprecated. Use the standard then method instead. If $httpProvider.useLegacyPromiseExtensions is set to false then these methods will throw $http/legacy error.

— AngularJS $http Service API Reference -- deprecation notice

UPDATE

The deprecated .success and .error methods have been removed from AngularJS 1.6.

Due to b54a39, $http's deprecated custom callback methods - .success() and .error() - have been removed. You can use the standard .then()/.catch() promise methods instead, but note that the method signatures and return values are different.

$http(...)
  .then(function onSuccess(response) {
    // Handle success
    var data = response.data;
    var status = response.status;
    var statusText = response.statusText;
    var headers = response.headers;
    var config = response.config;
    ...
  }).catch(function onError(response) {
    // Handle error
    var data = response.data;
    var status = response.status;
    var statusText = response.statusText;
    var headers = response.headers;
    var config = response.config;
    ...
  });

— AngularJS Developer Guide - Migrating to v1.6 - http

The pattern that javascript it using related to promises is only with .then(successCallback, errorCallback), so they are probably aiming to use js pattern.