Angular HttpPromise: difference between `success`/`error` methods and `then`'s arguments

There are some good answers here already. But it's worthwhile to drive home the difference in parallelism offered:

• success() returns the original promise
• then() returns a new promise

The difference is then() drives sequential operations, since each call returns a new promise.

$http.get(/*...*/).  then(function seqFunc1(response){/*...*/}).  then(function seqFunc2(response){/*...*/})

1. $http.get()
2. seqFunc1()
3. seqFunc2()

success() drives parallel operations, since handlers are chained on the same promise.

$http(/*...*/).  success(function parFunc1(data){/*...*/}).  success(function parFunc2(data){/*...*/})

1. $http.get()
2. parFunc1(), parFunc2() in parallel

NB This answer is factually incorrect; as pointed out by a comment below, success() does return the original promise. I'll not change; and leave it to OP to edit.

The major difference between the 2 is that .then() call returns a promise (resolved with a value returned from a callback) while .success() is more traditional way of registering callbacks and doesn't return a promise.

Promise-based callbacks (.then()) make it easy to chain promises (do a call, interpret results and then do another call, interpret results, do yet another call etc.).

The .success() method is a streamlined, convenience method when you don't need to chain call nor work with the promise API (for example, in routing).

In short:

• .then() - full power of the promise API but slightly more verbose
• .success() - doesn't return a promise but offeres slightly more convienient syntax

Some code examples for simple GET request. Maybe this helps understanding the difference.Using then:

$http.get('/someURL').then(function(response) {    var data = response.data,        status = response.status,        header = response.header,        config = response.config;    // success handler}, function(response) {    var data = response.data,        status = response.status,        header = response.header,        config = response.config;    // error handler});

Using success/error:

$http.get('/someURL').success(function(data, status, header, config) {    // success handler}).error(function(data, status, header, config) {    // error handler});