javascript - What does it mean to pass 2 functions into '.then()'? (Angular.js) -

i'm reading tutorial on angular.js , came across expression:

.then(handlerequest, handlerequest) 

i wondering mean pass 2 of same functions .then()?

here's more context:

function mainctrl(user, auth) {   var self = this;    function handlerequest(res) {     var token = res.data ? res.data.token : null;     if(token) { console.log('jwt:', token); }     self.message = res.data.message;   }    self.login = function() {     user.login(self.username, self.password)       .then(handlerequest, handlerequest)   }    ...  }  angular.module('app', []) .controller('main', mainctrl) .... })(); 

and original tutorial can found here: https://thinkster.io/angularjs-jwt-auth

first 1 successcallback , second 1 errorcallback.

// simple request example: $http({  method: 'get', url: '/someurl' }).then(function successcallback(response) { // callback called asynchronously // when response available }, function errorcallback(response) { // called asynchronously if error occurs // or server returns response error status. }); 

promises bit complex pattern understand. best resource me is

promises in angularjs, explained cartoon