The Horizon object instantiates and manages the connection to the Horizon server.

// connect to the Horizon server, after Horizon has been loaded via
// <script> tag or require
const hz = new Horizon();

Horizon constructor arguments

All arguments are optional. Pass them to Horizon in an object with option keys: {secure: true}.

  • host: the hostname of the Horizon server. This defaults to window.location, i.e., the machine that served the application to the client.
  • secure: a boolean indicating whether the server should use secure websockets. Defaults to true if static site is served via HTTPS, false otherwise.
  • path: the path the Horizon endpoint can be found under on host. Defaults to "horizon".
  • lazyWrites: a boolean indicating whether write operations should be performed in a “lazy” fashion (see below). Defaults to false.
  • authType: either a string indicating the authentication method to use for your application’s users, or a JSON Web Token to use for authentication. This is useful for bootstrapping the admin user, or for integrating with non-browser-based authentication methods.
    • Valid strings are "unauthenticated", "anonymous", or "token". Defaults to "unauthenticated".
    • To use a JWT, pass an object of the following form: {token: <TOKEN>, storeLocally: [true|false]}. If storeLocally is true (the default), the token will be stored in the browser’s local storage; if false, you’ll need to re-authenticate every time you create a Horizon object.
    • See Authentication for more information about authentication methods and token creation.

Lazy writes

When lazyWrites is set to true, Horizon queries that modify a Collection will not perform their writes when the query is first executed, but instead perform then when the Observable returned by the query is iterated through.

const hz = new Horizon({lazyWrites: true});

// because lazyWrites is set, nothing is sent to the server here...
var query = messages.store([
        from: "agatha",
        text: "Meet at Smugglers' Cove on Saturday"
        from: "bob",
        text: "Would Superman lose a fight against Wonder Woman?"

// ...but instead, writes are performed here
query.subscribe(uuid => {
    console.log('Document ${uuid} was created.');

A Horizon object can be called as a function, taking a string as its argument. It returns a Collection object:

// Return the messages Collection
const messages = hz('messages');



Establish a Horizon connection.

Note that you can create a Collection from the Horizon instance without calling connect() first. Once you start using the collection, the connection will be automatically established.

const hz = new Horizon();

// Get access to the messages collection
const messages = hz('messages');

// Start establishing the Horizon connection.
// This step is optional. We can skip it and go directly to the next line.

// Start using the collection
messages.store({ msg: 'Hello World!' });


Close a Horizon connection.


Receive status updates about the connection to the Horizon server.

Calling status() without any arguments returns an RxJS Observable. Alternatively you can pass in a callback to execute when the status of the connection changes. Any arguments passed to status() will be treated as if passed to Observable.subscribe(args...).

The emitted status objects can be one of the following:

  • { type: 'unconnected' }: The initial status before any connection has been established.
  • { type: 'connected' }: A websocket connection has been established. However the Horizon connection is not ready yet, since the Horizon handshake hasn’t been performed yet.
  • { type: 'ready' }: The Horizon instance is now fully usable.
  • { type: 'error' }: An error has occurred. A separate Error object with the specific error message will be emitted separately through the error callback (if any is subscribed on the Observable).
  • { type: 'disconnected' }: The websocket was closed.


Similar to Horizon.status(), but only emits { type: 'ready' } events.


Similar to Horizon.status(), but only emits { type: 'disconnected' } events.


Similar to Horizon.status(), but only emits { type: 'error' } events.


Check if the user has a valid authorization token (i.e., has logged in).

See Authentication for more details.


Returns a query for the current user, that you can run by calling either watch() or fetch().

The query result is a user object as described in Users and groups, or an empty object if the user is unauthenticated.

const hz = new Horizon();
hz.currentUser().fetch().subscribe( (user) => console.log(JSON.stringify(user)) );

currentUser() requires read permissions on the user’s document in the "users" collection. The following rule enables the required permissions:

template = "collection('users').find({id: userId()})"

See Permissions for more information on how to configure access rules, and Authentication to find out how to configure user authentication on the Horizon server.


Return a previously-configured OAuth endpoint.

See Authentication for more details.


Clear authentication tokens from local storage.


See Authentication for more details.


Combine the results of multiple Horizon queries into one result set.

const hz = new Horizon();

var userId = 100;
    userId: userId,
    user: hz('users').find(userId),
    activity: {
        posts: hz('posts').findAll({user: userId}),
        topComments: hz('comments').findAll({user: userId}).order('rating', 'descending').limit(10)

(In real code, subscribe() would contain a callback function to receive the Observable results from watch().)

The values for fields in aggregates may contain:

  • Horizon queries
  • Literals (as in the userId field above)
  • Objects (as in the activity field above)
  • Observables
  • Promises
  • Arrays

Observables inside an aggregate are called when the aggregate is subscribed to, and behave identically whether the aggregate is called with fetch() or watch(). So an aggregate such as the following:

    counter: Observable.timer(0, 1000),
    result: hz('foo').find('bar')
}).watch().subscribe({ next(x) { console.log(x) }});

will be emitted every time the document in the result query is changed and every time the counter is incremented.

Arrays are not flattened. A field/value such as dogShow: [hz('owners'), hz('pets')] will result in output similar to [['bob', 'agatha', ...], ['fluffy', 'fido', ...]]. (Use merge() for a union query.)

Aggregates can be nested, although this is equivalent to simply using objects for the “inner” aggregates.

/// this...
    foo: hz.aggregate({ ... })

// ...is equivalent to this
    foo: { ... }


Create a template for aggregates, using parameters.

The aggregate example could be rewritten with model this way:

const hz = new Horizon();

const userModel = hz.model((userId) => {
    return {
        userId: userId,
        user: horizon('users').find(userId),
        activity: {
            posts: horizon('posts').findAll({user: userId}),
            topComments: horizon('comments').findAll({user: userId}).order('rating', 'descending').limit(10)


You can do anything with model that you can do with aggregate, including nesting models.