AngularJS 1.2 sample on how to deal with errors on services returning always a Promise.

(function(undefined) {
    var app = angular.module('plunker', []);

    app.controller('MainCtrl', function($scope, Service) {
        Service.methodTest().then(success, error);

        Service.methodTest(123).then(success, error);

        function success(response) {
            console.log('resolved:', response);
        }

        function error(reason) {
            console.log('rejected:', reason);
        }
    });


    app.service('Service', function($q) {

        function methodTest(number) {
            
            // error path
            if (number === undefined) {
                return $q.reject(new Error('Missing parameter: number'));
            }
            
            
            // success path
            var def = $q.defer();
            
            def.resolve('Okay!');
            
            return def.promise;
        }


        return {
            methodTest: methodTest
        };
    });
    
    console.clear();
})()

<!DOCTYPE html>
<html ng-app="plunker">

  <head>
    <meta charset="utf-8" />
    <title>AngularJS Plunker</title>
    <script>document.write('<base href="' + document.location + '" />');</script>
    <link rel="stylesheet" href="style.css" />
    <script data-require="angular.js@1.2.x" src="https://code.angularjs.org/1.2.21/angular.js" data-semver="1.2.21"></script>
    <script src="app.js"></script>
  </head>

  <body ng-controller="MainCtrl">
    <p>Check the console!</p>
  </body>

</html>

/* Put your css in here */