An interface for defining custom smart cells.

A smart cell is a UI wizard designed for producing a piece of code that accomplishes a specific task. In other words, a smart cell is like a code template parameterized through UI interactions.

This module builds on top of Kino.JS.Live, consequently keeping all of its component and communication mechanics. The additional callbacks specify how the UI maps to source code.

usage

Usage

Defining a custom cell is similar to writing a regular Kino.JS.Live component, with a couple specifics.

First, we only need to define callbacks, so there is no need for using Kino.JS.Live.new/2. The Kino.JS.Live.init/2 callback always receives attrs/0 as the first argument.

Second, we add a few new bits, namely use Kino.SmartCell and the two corresponding callback definitions.

Here is an outline of a custom module

defmodule Kino.SmartCell.Custom do
  use Kino.JS
  use Kino.JS.Live
  use Kino.SmartCell, name: "Our custom wizard"

  @impl true
  def init(attrs, ctx) do
    ...
  end

  # Other Kino.JS.Live callbacks
  ...

  @impl true
  def to_attrs(ctx) do
    ...
  end

  @impl true
  def to_source(attrs) do
    ...
  end
end

Additionally, in order for Livebook to pick up the custom cell, we need to register our module. This usually happens in application.ex

Kino.SmartCell.register(Kino.SmartCell.Custom)

example

Example

As a minimal example, that's how we can define a cell that allows editing the underlying code directly through a textarea.

defmodule Kino.SmartCell.Plain do
  use Kino.JS
  use Kino.JS.Live
  use Kino.SmartCell, name: "Plain code editor"

  @impl true
  def init(attrs, ctx) do
    source = attrs["source"] || ""
    {:ok, assign(ctx, source: source)}
  end

  @impl true
  def handle_connect(ctx) do
    {:ok, %{source: ctx.assigns.source}, ctx}
  end

  @impl true
  def handle_event("update", %{"source" => source}, ctx) do
    broadcast_event(ctx, "update", %{"source" => source})
    {:noreply, assign(ctx, source: source)}
  end

  @impl true
  def to_attrs(ctx) do
    %{"source" => ctx.assigns.source}
  end

  @impl true
  def to_source(attrs) do
    attrs["source"]
  end

  asset "main.js" do
    """
    export function init(ctx, payload) {
      ctx.importCSS("main.css");

      ctx.root.innerHTML = `
        <textarea id="source"></textarea>
      `;

      const textarea = ctx.root.querySelector("#source");
      textarea.value = payload.source;

      textarea.addEventListener("change", (event) => {
        ctx.pushEvent("update", { source: event.target.value });
      });

      ctx.handleEvent("update", ({ source }) => {
        textarea.value = source;
      });

      ctx.handleSync(() => {
        // Synchronously invokes change listeners
        document.activeElement &&
          document.activeElement.dispatchEvent(new Event("change"));
      });
    }
    """
  end

  asset "main.css" do
    """
    #source {
      box-sizing: border-box;
      width: 100%;
      min-height: 100px;
    }
    """
  end
end

And then we would register it as

Kino.SmartCell.register(Kino.SmartCell.Plain)

Note that we register a synchronization handler on the client with ctx.handleSync(() => ...). This optional handler is invoked before evaluation and it should flush any deferred UI changes to the server. In our example we listen to textarea's "change" event, which is only triggered on blur, so on synchronization we trigger it programmatically.

collaborative-editor

Collaborative editor

If a smart cell requires editing some code (like SQL), it may use a dedicated editor instance managed by Livebook. The editor handles syntax highlighting and collaborative editing, similarly to the built-in cells.

To enable the editor, we need to include :editor configuration in options returned from the Kino.JS.Live.init/2 callback.

@impl true
def init(attrs, ctx) do
  # ...
  {:ok, ctx, editor: [attribute: "code", language: "elixir"]}
end

options

Options

• :attribute - the key to put the source text under in attrs. Required

• :language - the editor language, used for syntax highlighting. Defaults to nil

• :placement - editor placement within the smart cell, either :top or :bottom. Defaults to :bottom

• :default_source - the initial editor source. Defaults to ""

other-options

Other options

Other than the editor configuration, the following options are supported:

• :reevaluate_on_change - if the cell should be reevaluated whenever the generated source code changes. This option may be helpful in cases where the cell output is a crucial element of the UI interactions. Defaults to false