Example of angular resolve with "class" resolve and ensuring data is current on every route change.

angular-resolve.js

(function() {
"use strict";

angular.module('JobListingApp')
.config(['$routeProvider', function($routeProvider) {
    // ListingRoute "class" to ensure that all routes have
    // current data in JobListings before they execute a route's controllers
    var ListingRoute = function(params) {
        angular.extend(this, params);
    };
    ListingRoute.prototype.resolve = {
        listings: ['JobListings', function(JobListings) {
            return JobListings.ensure_current();
        }]
    };

    // each route is an instance of ListingRoute,
    // each has the same resolve property
    $routeProvider
    .when("/listings", new ListingRoute({
        templateUrl: "partials/listings.html",
        controller: "ListingsCtrl"
    }))
    .when("/listings/:id", new ListingRoute({
        templateUrl: "partials/listing.html",
        controller: "ListingCtrl"
    }))
    .otherwise({redirectTo: '/listings'});
}])
.factory('JobListings', ['$http', '$q', function($http, $q) {
    var JL = {data: null};
    JL.ensure_current = function() {
        var self = this,
            data_deferred = $q.defer();
        if (self.data) {
            // for every call after the first call,
            // promise is resolved immediately
            data_deferred.resolve(self.data);
        } else {
            $http.get('/api/job-listings').success(function(data) {
                self.data = data;
                // promise is resolved after API GET
                data_deferred.resolve(data);
            }).error(function() {
                //redirect someplace? authorize?
            });
        }
        // promise is immediately returned
        // route controller will not execute until promise is resolved
        return data_deferred.promise;
    };
    return JL;
}])
;
})();

Why go through the process of creating a class, constructor and then using prototype? Why not put the listings method right on resolve? Is there some sort of perf benefit?

var listings = ['JobListings', function(JobListings) {
            return JobListings.ensure_current();
        }];
...
    .when("/listings",
        templateUrl: "partials/listings.html",
        controller: "ListingsCtrl",
        resolve: listings
    )