Your first Supler form


Let’s say we have the following class on the backend:

case class Person(name: String, age: Int, address: Option[String], likesChocolate: Boolean)

A form backed by instances of the Person class for editing a user’s details can then have the following definition:

import org.supler.Supler._

val personForm = form[Person](f => List(
  f.field(_.age).label("Age").validate(gt(1), le(150)),
  f.field(_.likesChocolate).label("Do you like chocolate?"),
  f.action("save") { p =>
    println("Saving person: " + p)

As you can see, a form contains a list of fields. Here we are using a convenience function, form, to capture the class of the object once, so that we can later specify the fields using closures like: _.fieldName, without any type annotations.

Each field can be customized. For example, here every field has a label. Also, the age field has two validators: age must be > 1 and <= 150 (we are optimistic about the development of education and medicine). All fields which are not wrapped in an Option have also a “required” validation added.

Finally, besides the four fields, we have an action, which - as the label probably reveals - is supposed to save the form. Here we just print the object to the console. How you handle actions, and how you actually “save” objects is up to you, all you need to do is provide a closure accepting the modified data. We also specify that to invoke the action, the whole form must be valid (using validateAll()).

The result of the save action is a custom JSON. Supler uses json4s for parsing & creating JSON with the native backend; in fact, it is the only dependency of Supler. The custom JSON in this case is just a string message, “Saved” (presumably to be displayed to the user on the frontend).

Having the form defined, we need to expose it to the world, which is typically done using some web or REST framework. You can use servlets with JAX-RS, Spray, Play, Scalatra, or any custom framework you want. To keep the tutorial simple, let’s assume we have two methods mapped to appropriate paths & http methods:

  • getPersonForm(): JValue, invoked on a GET /personform
  • postPersonForm(body: JValue): JValue, invoked on a POST /personform with the body parsed as JSON

The implementation of get is quite straightforward:

def getPersonForm(): JValue = {
  val person = lookupCurrentPerson()

Again, where do the specific Person instances come from, do they come from the session, or if they are looked up basing on HTTP parameters, is outside the scope of Supler.

Once we have a Person instance, we apply it to the form (personForm(person)), and generate the JSON description of the form, reading field values from the given object (if you are curious how the JSON looks like, check out the JSON section of the docs).

The post method is similarly simple:

def postPersonForm(body: JValue): JValue = {
  val person = lookupCurrentPerson()

What process does is:

  • convert and apply values from the given json to the person object
  • run validations
  • if there are no errors, run the actions (if any)

If no action is invoked (body has only field value mappings), this method can be used for doing server-side validation of a form; the result will contain any validation errors, which can be the displayed to the user. In our example, if the "save" action was invoked and the data was valid, the result of process(body).generateJSON would be the action’s result: JString("Saved").

You can also invoke any of the processing steps by hand; this is covered later in the docs.


Time to display something! First we need a designated space on our HTML page where the form will be displayed:

  <script src="/supler.js"></script>
  <div id="person_form_container"></div>

Then, when the page opens, we need to fetch and display the form. I will use JQuery here, but of course any way of doing AJAX calls/networking will work, JQuery is not a dependency of Supler:

var form = new Supler.Form(

$(document).ready(function() {
  $.get('/personform', function(data) {

Here we are creating a Supler.Form instance which as the first arguments requires the HTML element where the form should be rendered, and as the second options, which we’ll be using shortly. Then, when the document is ready, we are calling the endpoint to get the JSON form description, and we render the results. This will display a 4-field & 1-button form to the user.

What about sending user changes, when an action is invoked (in our case, when the “Save” button is clicked)? Supler doesn’t contain any code to e.g. perform AJAX requests. Instead, we need to to provide a way to send data back to the backend. This is configured via the send_form_function option, which is an integration point with whatever way of doing network communication we are using:

var form = new Supler.Form(
    send_form_function: sendForm

function sendForm(formValue, renderResponseFn, sendErrorFn) {
    url: '/personform',
    type: 'POST',
    data: JSON.stringify(formValue),
    dataType: 'json',
    contentType: 'application/json; charset=utf-8',
    success: renderResponseFn,
    error: sendErrorFn

This is a fairly standard JQuery AJAX call. What is important, is that we are POSTing the form value (received as a parameter) serialized as JSON to the backend, and for handling responses we are using the provided renderResponseFn which will re-render the form if there are conversion/validation errors.

After a field is edited, and before an action is invoked, client-side validations are run. If they fail, a message is displayed to the user. Of course, validations are also run on the server, before actually running the action code.

Not all validations are both client- and server-side. Most of the built-in are, but you can also provide custom validations, which are server-side only, or which perform a simplified client-side validation.

Finally, what if an action returns a custom JSON? This must be handled somehow as well. We need to provide a method which will handle such responses:

var form = new Supler.Form(
    send_form_function: sendForm,
    custom_data_handler: function(data) {

And that’s it! Like on the server-side, you can call any of the stages (serializing a form to JSON, validating, re-rendering with new data) by hand; this will also be covered later in the docs.

What’s next?

The various Supler components are described in more detail in further sections. If you’d like to add Supler to your project, head over to setup. If you have any questions, feel free to ask on the forum.