Angular $http service with automatic retries and status code based error messages

services.js

(function (app) {
    // Fluent interface to generate a map of status codes to error messages
    function genErrorMap() {
        var statusErrorMap = { "default": { msg: "An error has occurred", retryable: false } };

        var methods = {
            // Add a mapping from an array of status codes to an errorMessage and whether we should retry
            // the request when recieving this error status code
            add: function (statusCodes, errorMessage, retryable) {
                for (var i = 0; i < statusCodes.length; i++) {
                    statusErrorMap[statusCodes[i]] = { msg: errorMessage, retryable: retryable || statusErrorMap.default.retryable };
                }
                // return methods again so calls can be chained: add(...).add(...).add(...)
                return methods;
            },
            setDefault: function(msg, retryable) {
                var defaultInfo = statusErrorMap.default;
                defaultInfo.msg = msg;
                defaultInfo.retryable = retryable || false;

                return methods;
            },
            value: function () { return statusErrorMap; }
        }

        return methods;
    }

    // Generate an error handler with automatic retries
    function generateErrorHandler($log, errorMapping, deferred, retryFn, originalArgs, retryPosition) {
        var retries = originalArgs[retryPosition] || 0;

        return function (msg, code) {
            $log.error(msg, code);

            var thisHandler = errorMapping[code] || errorMapping.default;
            if (retries < 3 && thisHandler.retryable) {
                // increment retries
                originalArgs[retryPosition] = retries + 1;
                var chainedDefer = retryFn.apply(this, originalArgs);
                chainedDefer.then(function (chainedResult) { deferred.resolve(chainedResult); },
                    function (chainedError) { deferred.reject(chainedError); });
            } else {
                deferred.reject(thisHandler.msg);
            }
        };
    };

    var todoService = function ($http, $log, $q) {
        // Keep a local reference to the array so we can dynamically update it
        var todos = [];
        var methods = {
            // Give a reference to the controller for the array we will update asyncronously
            initialize: function () { return todos; },
            // Refresh the list of todos and return so contollers can have a reference
            index: function () {
                // Create a deferred object that can be returned immediately
                // We keep this separate from the $http deferred object so that we 
                // can do things like retry without notifying the client (in this case an angular
                // controller) that we have failed until we give up completly
                var deferred = $q.defer();

                // Define status code to error mapping
                var errorMapping = genErrorMap()
                    .add([401, 403], "You do not have permission to access todos")
                    .add([408, 503, 429], "There was a problem connecting to the server. Please refresh the page & try again after a few minutes", true)
                    .setDefault("There was an application error. If the problem persists please contact support")
                    .value();

                $http.get("/api/Todos")
                    .success(function (data) {
                        todos.length = data.length;
                        for (var i = 0; i < data.length; i++) {
                            // If our data model did not match this is where we could modify it 
                            todos[i] = data[i];
                        }
                        // Mark the async action as completed and return todos
                        // Likely the controller already receieved a reference to todos
                        // using the init method, but is here for convinience in case.
                        deferred.resolve(todos);
                    }).error(generateErrorHandler( $log, errorMapping, deferred, methods.index, arguments, 0));

                return deferred.promise;
            }
        };

        return methods;
    };

    // setup dependencies 
    // see https://github.com/johnpapa/angularjs-styleguide#style-y091 for explanation
    todoService.$inject = ["$http", "$log", "$q"];
    // register the factory so it can be used with dependency injection
    app.factory("TodoService", todoService);

})(angular.module("todomvc",[]));