Server protocol

Communication between server and client consists of asynchronous calls to load and save data. The server is expected to provide a RESTful interface using resource-oriented URLs that can be accessed by HTTP methods GET, POST, PUT and DELETE, respectively. Data serialisation for transport uses the JSON format.

Loading data

Data can be loaded in one of two ways: by requesting it from the resource URL, or by passing it as an argument to the form object upon initialisation.

Either way, the data format is a mapping of field names to values. Values may be any data type known to the JSON format, or appropriate serialisations that can be JSON-encoded, see the explanation of datatypes. If the form object is initialised with a URL instead of a field-value mapping, an XHR GET request is sent to the URL and the full response is expected to be the JSON-encoded field-value mapping:

{firstname: "Jack", lastname: "", send_notifications: true, messages: 0}

Storing changes


With the current client implementation, each field will send its own value to the server separately after it lost focus. To do so, a JSON-encoded mapping of field name to value (or an appropriate representation thereof) is sent to the resource URL by an XHR POST request:

{firstname: "John"}

In fact, this is an instance where the current implementation doesn’t strictly assume a RESTful URL layout; there may be different URLs for loading and saving form data. The URL for saving is specified by the save_url form option; if the form object was initialised with a load URL instead of initial data, the save_url option may be omitted and will default to the load URL. The latter special case of a single resource URL does imply a RESTful server.

Since the request body contains a mapping from field name to value, this allows for more than one field value to be stored at the same time. While the stock implementation doesn’t store the value of more than one field through the same request, custom widgets may do so; also, a CSRF token may be sent along under a configurable name. A server implementation must assume any number of fields to be sent within one save request.


The HTTP response code may be 200 if everything went fine technically (even though validation errors may have occurred), or some error code if a server or connection error occurred. In that case, a notification is displayed to the user and the save request is queued to be retried later.

The body of a response with status 200 must be a JSON-encoded mapping that contains at least a status flag, signifying whether validation succeeded. Upon success, the minimal body should read:

{status: "success"}

In the case of validation errors, the response is expected to convey an error message suitable to present to the user, e.g.

{status: "error", msg: "Not a valid email address"}

The error message will be displayed by the widget that initiated the save request.

Updating sources

Furthermore, the response body for a successful save request may contain updated sources for object fields within the same form. This is to help with interdependent widgets where the value of a field determines the set of possible choices of one or more dependent fields.

If a saved value results in updates to any sources for other fields within the form, the response body contains another key sources whose value is a mapping from field names to new source values. Source values have the same format (lists of objects having a token and title) as when configuring them statically through the form options:

{status: "success",
 sources: {subcategories: [
     {token: "sub-a1", title: "Subcategory A.1"},
     {token: "sub-a2", title: "Subcategory A.2"}


The data format to load a collection is a list of items. Items are objects containing a resource url, which points to the RESTful interface of that item, and an object with item data, that will be displayed inside the collection:

    {resource: 'message/1',
     data: {'title': 'The title', 'description': 'The description'},
    {resource: 'message/2',
     data: {'title': 'Another title', 'description': 'Another description'}

The collection protocol is identical for all collection widgets.