Angular.js countdown timer directive

gistfile1.js

/*
 * AngularJS Countdown Timer Directive
 * Author: Rob Anderson @iotaweb
 * Dependencies: https://github.com/EvanHahn/HumanizeDuration.js
 * Example: <span countdown class="pull-right" prefix="Token expires in" expires="{{ token.expiresAt }}"></span>
 */
(function () {

    'use strict';

    angular
        .module('app')
        .directive('countdown', countdown);

    function countdown ($interval, auth) {

        return {
            restrict: 'A',
            scope: {
                prefix: '@',
                expires: '@'
            },
            link: function (scope, element) {

                var expiresAt = parseInt(scope.expires, 10);
                var prefix = '';

                if (scope.prefix) {
                    prefix = scope.prefix + ' ';
                }

                scope.$watch('expires', function () {

                    expiresAt = parseInt(scope.expires, 10);
                });

                $interval(function () {

                    var remaining = expiresAt - Math.floor(Date.now() / 1000);

                        return element.text(prefix + humanizeDuration(remaining * 1000, {
                            halfUnit: false
                        }));
                }, 1000);
            }
        };
    }
})();