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

Monthly Downloads: 366
Programming language: Elixir
License: MIT License
Tags: UI     HTML     jQuery    
Latest version: v0.10.5

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Build Status hex.pm version hex.pm downloads API Docs Inline docs Ebert

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 <%= @progress_bar_class %>" role="progressbar" @style.width=<%= "#{@bar_width}%" %>>
    <%= "#{@bar_width}%" %>
<button class="btn btn-primary" drab-click="perform_long_process">
  <%= @long_process_button_text %>
  • Server side:
defhandler perform_long_process(socket, _sender) do
  poke socket, progress_bar_class: "progress-bar-danger", long_process_button_text: "Processing..."

  steps = :rand.uniform(100)
  for i <- 1..steps do
    Process.sleep(:rand.uniform(500)) #simulate real work
    poke socket, bar_width: Float.round(i * 100 / steps, 2)

  poke socket, progress_bar_class: "progress-bar-success", long_process_button_text: "Click me to restart"


  1. Elixir ~> 1.6.0 (see Installation Guide)

  2. Phoenix ~> 1.2 (see Installation Guide)

Browser Requirements

This has the same requirements as Phoenix.Sockets. Above that it depends on the javascript you call or other potential tools you use on top of Drab.


First of all, you need to have a Phoenix application, on top of which you will install Drab. If this is a standard app, generated with mix phx.new, you may use Drab Installer to make it running in one, simple step. Otherwise, see Manual Installation section below.

  1. Edit mix.exs in the main folder in your web application (if you have multiple application under an umbrella, this is the one ending with _web). Locate function deps (search for def deps string). Add an entry {:drab, "~> 0.10.0"} to the list. Don't forget about comma!
def deps do
    {:drab, "~> 0.10.0"}
  1. Download and install packages:
$ mix deps.get
  1. Go to the application directory (if your Phoenix Web application is under the umbrella, go there) and run mix drab.install:
bash% mix drab.install
Checking prerequisites for :my_app
The installer is going to modify those files. OK to proceed? [Yn] Y
Drab has been successfully installed in your Phoenix application.

Now it is time to create your first commander, for example, for PageController:

    mix drab.gen.commander Page

Congratulations! You have installed Drab and you can proceed with your own commander.

Please notice that Drab will run only on pages, which have the corresponding commander.


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 pages generated with corresponding controller, you need to create a twin commander. For example, for MyApp.PageController the commander should be named MyApp.PageCommander.

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

  1. Generate the page Commander. The commander name should correspond to the controller, so PageController should have PageCommander:
$ mix drab.gen.commander Page
* creating web/commanders/page_commander.ex
  1. Add the @welcome_text assign to render/3 in index action in the controller, to be used in the future:
defmodule MyApp.PageController do
  use Example.Web, :controller

  def index(conn, _params) do
    render conn, "index.html", welcome_text: "Welcome to Phoenix!"
  1. Rename the template from web/templates/page/index.html.eex to index.html.drab

  2. Edit the template web/templates/page/index.html.drab and change the fixed welcome text to the assign:

<div class="jumbotron">
  <h2><%= @welcome_text %></h2>
  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 the Drab server:
defmodule DrabExample.PageCommander do
  use Drab.Commander

  onload :page_loaded

  # Drab Callbacks
  def page_loaded(socket) do
    poke socket, welcome_text: "This page has been drabbed"
    set_prop socket, "div.jumbotron p.lead",
      innerHTML: "Please visit <a href='https://tg.pl/drab'>Drab</a> page for more"

The poke/2 function updates the assign. The set_prop/3 updates any property of the DOM object. All is done live, without reloading the page.

  1. Run iex -S mix phoenix.server. Go to http://localhost:4000 to see the changed web page. Now you may play with this page live, directly from iex! Observe the instruction given when your browser connects to the page:
    Started Drab for same_path:/, handling events in DrabExample.PageCommander
    You may debug Drab functions in IEx by copy/paste the following:
import Drab.{Core, Element, Live}
socket = Drab.get_socket(pid("0.653.0"))

socket |> exec_js("alert('hello from IEx!')")
socket |> poke(count: 42)

As instructed, copy and paste those two lines, and check out yourself how you could remotely control the displayed page:

iex> alert socket, "Alert title", "Do you like modals?", buttons: [ok: "A juści", cancel: "Poniechaj"]
{:ok, %{}}

iex> poke socket, welcome_text: "WOW, this is nice"

iex> query socket, "div.jumbotron h2", :innerText
 %{"[drab-id='425d4f73-9c14-4189-992b-41539377c9eb']" => %{"innerText" => "WOW, this is nice"}}}

iex> set_style socket, "div.jumbotron", backgroundColor: "red"
{:ok, 1}

The example above is available here

What now?

Visit Demo Page for a live demo and more description.

Visit Documentation page.

Getting help

There is a Drab's thread on elixirforum.com, please address questions there.

Tests and Sandbox

Since 0.3.2, Drab is equipped with its own Phoenix Server for running integration tests automatically, for sandboxing and for playing with it.


  • clone Drab from github:
git clone [email protected]:grych/drab.git
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, Live, Element, Query, Waiter}
socket = Drab.get_socket(pid("0.784.0"))

iex> query socket, "h3", :innerText
 %{"#header" => %{"innerText" => "Drab Tests"},
   "#page_loaded_indicator" => %{"innerText" => "Page Loaded"}}}

iex> set_prop socket, "h3", innerText: "Updated from IEx"
{:ok, 2}

iex> exec_js socket, "alert('You do like alerts?')"
{:ok, nil}


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

  • clone Drab from github:
git clone [email protected]:grych/drab.git
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 23 files (.ex)

Finished in 120.9 seconds
123 tests, 0 failures

Randomized with seed 934572

Manual Installation

  1. Add Drab to the dependencies in mix.exs.

  2. Initialize Drab client library by adding to the layout page (app.html.eex - or any other layout you use).

<%= Drab.Client.run(@conn) %>

just after the following line:

<script src="<%= static_path(@conn, "/js/app.js") %>"></script>
  1. Initialize Drab sockets by adding the following to user_socket.ex:
use Drab.Socket
  1. Add Drab template engine and application name with endpoint to config.exs:
config :phoenix, :template_engines,
  drab: Drab.Live.Engine

config :drab, MyAppWeb.Endpoint,
  otp_app: :my_app_web
  1. Add :drab to applications started by default in mix.exs:
def application do
  [mod: {MyApp, []},
   applications: [:phoenix, :phoenix_pubsub, :phoenix_html, :cowboy, :logger, :gettext, :drab]]

It is not needed if you are running Phoenix 1.3

  1. To enable live reload on Drab pages, add .drab extension to live reload patterns in dev.exs:
config :my_app, MyApp.Endpoint,
  live_reload: [
    patterns: [
  1. If you are not using webpack, you will get require is not defined error. You need to provide Socket:

In the app.js add a global variable, which will be passed to Drab later:

  window.__socket = require("phoenix").Socket;

Then, tell Drab to use this instead of default require("phoenix").Socket. Add to config.exs:

config :drab, MyAppWeb.Endpoint,
  js_socket_constructor: "window.__socket"

If you want to use Drab.Query (jQuery based module):

  1. Add jquery and boostrap to package.json:
"dependencies": {
  "jquery": ">= 3.1.1",
  "bootstrap": "~3.3.7"
  1. Add jQuery as a global at the end of brunch-config.js:
npm: {globals: {
  $: 'jquery',
  jQuery: 'jquery',
  bootstrap: 'bootstrap'
  1. And install it:
$ npm install && node_modules/brunch/bin/brunch build


(c)2016-2018 Tomek "Grych" Gryszkiewicz, [email protected]

Illustrations by https://www.vecteezy.com