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grych / drab


Manipulate User Interface directly from the Elixir/Phoenix application: eliminate Ajax and JS


phoenix logo version downloads API Docs

See Demo Page for live demo and description.

Drab - Access the browser User Interface from the Server Side. No Javascript programming needed anymore!

Drab extends Phoenix Framework to "remote control" UI on the browser, live. The idea is to move all User Interface logic to the server-side, to eliminate Javascript and Ajax calls.


  • Client side:
<div class="progress">
  <div class="progress-bar" role="progressbar" style="width:0%">
<button drab-click="perform_long_process">Click to start processing</button>
  • Server side:
def perform_long_process(socket, dom_sender) do
  steps = MyLongProcess.number_of_steps()
  for i <- 1..steps do
    # update the progress bar after each of MyLongProcess steps
      |> update(
          css: "width", 
          set: "#{i * 100 / steps}%", 
          on: ".progress-bar")
      |> update(
          set: "#{Float.round(i * 100 / steps, 2)}%", 
          on: ".progress-bar")
  socket |> insert(class: "progress-bar-success", into: ".progress-bar")


  1. Erlang ~> 19

  2. Elixir ~> 1.3

  3. Phoenix ~> 1.2


So far the process of the installation is rather manually, in the future will be automatized.

  1. Add drab to your list of dependencies in mix.exs in your Phoenix application and install it:
def deps do
  [{:drab, "~> 0.3"}]
$ mix deps.get
$ mix compile
  1. Add jquery and boostrap to package.json:
"dependencies": {
  "jquery": ">= 3.1.1",
  "bootstrap": "~3.3.7"

You may ommit this step if you are not planning to use DOM, jQuery, Drab.Query and Drab.Modal - see Domless Drab

  1. Add jQuery as a global at the end of brunch-config.js:
npm: {globals: {
  $: 'jquery',
  jQuery: 'jquery',
  bootstrap: 'bootstrap'

You may ommit this step if you are not planning to use DOM, jQuery, Drab.Query and Drab.Modal - see Domless Drab

  1. And install it:
$ npm install && node_modules/brunch/bin/brunch build 
  1. Initialize Drab client library by adding to the layout page (web/templates/layout/app.html.eex)
<%= Drab.Client.js(@conn) %>
just after the following line:
<script src="<%= static_path(@conn, "/js/app.js") %>"></script>
  1. Initialize Drab sockets by adding the following to web/channels/user_socket.ex:
use Drab.Socket

Congratullations! You have installed Drab and you can proceed with your own Commanders.


All the Drab functions (callbacks, event handlers) are placed in the module called Commander. Think about it as a controller for the live pages. Commanders should be placed in web/commanders directory.

To enable Drab on the specific pages, you need to add the directive use Drab.Controller to your application controller.

Remember the difference: controller renders the page while commander works on the live page.

  1. Generate the page Commander. Commander name should correspond to controller, so PageController should have PageCommander:
$ mix drab.gen.commander Page
* creating web/commanders/page_commander.ex

Add the following line to your Example.PageController:
    use Drab.Controller 
  1. As described in the previous task, add Drab.Controller to your page Controller (eg. web/controllers/page_controller.ex in the default app):
defmodule DrabExample.PageController do
  use Example.Web, :controller
  use Drab.Controller 

  def index(conn, _params) do
    render conn, "index.html"
  1. Edit the commander file web/commanders/page_commander.ex and add some real action - the onload callback which fires when the browser connects to Drab.
defmodule DrabExample.PageCommander do
  use Drab.Commander

  onload :page_loaded

  # Drab Callbacks
  def page_loaded(socket) do
      |> update(:html, set: "Welcome to Phoenix+Drab!", on: "div.jumbotron h2")
      |> update(:html, 
          set: "Please visit <a href=''>Drab</a> page for more examples and description",
          on:  "div.jumbotron p.lead")

Function update/3 (shorthand for Drab.Query.update/3) with :html parameter sets the HTML of DOM object, analogically to $().html() on the client side.

Finally! Run the phoenix server and enjoy working on the Dark Side of the web.

All above is available for download here

Drab Events

  • Client-side: assign the events directly in HTML, using drab-event=event_name and drab-handler='event_handler' combination of attributes, when event_name is the JS event name and event_handler is the function name in the Commander. This function will be fired on event. There is also a shorthand for this: drab-[event_name]=event_handler (currently: click, change, keyup, keydown are defined). Example:
<button drab-click='button_clicked'>Clickme!</button>
  • Server-side: when clicked, this button will launch the following action on the corresponding commander:
defmodule Example.PageCommander do
  use Drab.Commander

  # Drab Events
  def button_clicked(socket, dom_sender) do
      |> update(:text, set: "alread clicked", on: this(dom_sender))

As you probably guess, this changes button description (Drab.Query.update/3 used with :text).

What now?

Visit Demo Page for a live demo and more description.

Visit Docs with Examples - documentation with short examples.

Tests and Sandbox

Since 0.3.2, Drab is equipped with its own Phoenix Server for automatic integration tests and for sandboxing and play with it.


  • clone Drab from github:
git clone
cd drab
  • get deps and node modules:
mix deps.get
npm install && node_modules/brunch/bin/brunch build
  • start Phoenix with Drab:
iex -S mix phoenix.server
  • open the browser and navigate to http://localhost:4000

  • follow the instructions in IEx to play with Drab functions:

import Drab.Core; import Drab.Query; import Drab.Modal; import Drab.Waiter
socket = Drab.get_socket(pid("0.443.0"))

iex(5)> socket |> alert("Title", "WOW!")                                          
{:ok, %{}}
iex(6)> socket |> select(:text, from: "h3")
"Drab Tests"
iex(7)> socket |> update(:text, set: "It is set from IEx, wow!", on: "h3")  
%Phoenix.Socket{assigns: %{__action: :index, .........


Most of the Drab tests are integration (end-to-end) tests, thus they require automated browser. Drab uses chromedriver, which must be run while you run tests.

  • clone Drab from github:
git clone
cd drab
  • get deps and node modules:
mix deps.get
npm install && node_modules/brunch/bin/brunch build
  • run chromedriver

  • run tests:

$ mix test
Compiling 29 files (.ex)

Generated drab app

Finished in 149.4 seconds
71 tests, 0 failures

Randomized with seed 277485


(c)2016 Tomek "Grych" Gryszkiewicz,

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