How do I handle page refreshing with an AngularJS Single Page Application

Question

Two problems have troubled me as I have learned angular:

1. How do I restore state when the user refreshes the page or hits the back button?

2. How do I share data between scopes belonging to different controllers?

Below I show a simple solution that makes use of client-side session storage. It allows for both the sharing of common data and the automatic restoration of state after a user refreshes the page or hits the back button.

Note: The solution below proved essential to answer the following question:

How do I get the Back Button to work with an AngularJS ui-router state machine?

Answer 1

The solution depends on the SessionService class shown below. The syntax is coffeescript.

SessionService Class

class SessionService
    scopes:[]

    setStorage:(key, value) ->
        scope[key] = value for scope in @scopes
        value =  if value is undefined then null else JSON.stringify value
        sessionStorage.setItem key, value

    getStorage:(key)->
        sessionValue = sessionStorage.getItem key
        if sessionValue == "undefined"
            return null
        JSON.parse sessionValue

    register:(scope)->
        for key, value of sessionStorage
            scope[key] = if value? and value != "undefined" then JSON.parse(value) else null
        @scopes.push scope
        scope.$on '$destroy', =>
            @scopes = @scopes.filter (s) -> s.$id != scope.$id

    clear: ->
        @setStorage(key, null) for key of sessionStorage

    isAuthenticated: ->
        @accessor 'isAuthenticated', value

    user:(value=null) ->
        @accessor 'user', value

    # other storage items go here 

    accessor:(name, value)->
        return @getStorage name unless value?
        @setStorage name, value

angular
.module 'app.Services'
.service 'sessionService', SessionService

The SessionService class defines the isAuthenticated property (simple bool) and the user property (a complex object) . The values of these properties are automatically stringified / parsed as they are stored / retrieved using the client-side local sessionStorage object supplied by javascript.

You add more properties as required. Like $rootScope you add properties sparingly. Unlike $rootScope the property values are still available after a page refresh or back button click.

The service allows any number of scopes to be registered with it. When a scope is registered all the stored values in sessionStorage are automatically assigned to that scope. In this way all the registered scopes always have access to all the session properties.

When a property value is updated, all the registered scopes have their corresponding values updated.

When angular destroys a scope it is automatically removed from the list of registered scopes to save wasting resources.

If a user refreshes the page or hits the back button then the angular application is forced to restart. Normally this would mean you would have to reconstruct your current state. The SessionService does this for you automatically as each scope will have its values restored from local storage when they are registered during the app initialisation.

So now it is easy to solve the problem of both sharing data between scopes as well as restoring values when the user refreshes or hits the back button.

Here is some sample angular code that shows how to use the SessionService class.

Register a scope with SessionService in some Controller

angular
.module 'app'
.controller 'mainCtrl', ($scope, $state, session, security) ->
    #register the scope with the session service
    session.register $scope

    #hook up the 'login' method (see security service)
    $scope.login = security.login

    # check the value of a session property
    # it may well be true if the page has been refreshed
    if session.isAuthenticated
        $state.go('home')
    else
        $state.go('login')

Set Session values in a service

 class SecurityService
    @$inject:['$http','sessionService', 'api']
    constructor:(@http, @session, @api) ->

    login:(username, password) =>
        @http.get "#{@api.base}/security/login/credentials/#{username}/#{password}"
        .success (user)=>
            @session.isAuthenticated = true
            @session.user = user
        .error (ex)=>
            # process error

angular
.module 'app'
.service 'securityService', SecurityService

Use Session values in UI (Jade template)

div(ng-show="isAuthenticated")
    div Hello {{user.Name}}

Answer 2

I was faced with the same issue and chose to use angular cookies, since the only state that is not pulled by the template via ng-init is the logged in user state.

I store the user ID in a cookie on login after I've received the user model from our server and I clear the user ID cookie on logout. Then to recover the logged in user state on a page refresh or back button event, I hook the $location service's $locationChangeStart event. From my experimentation, this event is triggered at the point the location is about to change but before the partial/template has been loaded. This allows the needed state to be loaded just in time.

I'm not convinced that I don't have a race condition here as $scope.loadLoggedInUser(...) uses asynch $http to load the needed state but so far it has worked reliably for me.

$scope.$on('$locationChangeStart', function() {
            $log.debug("locationChangeStart");
            if (!$scope.appCtx.models.loggedInUser) {
                var userID = $cookies.get("userID");
                if (!userID) {
                    $scope.doLogout();
                    return;
                }
                $scope.loadLoggedInUser(userID, true);
            }
        });