opal-jquery offers a nicer ruby-like syntax for JQuery. It is useful for projects which cannot use opal-browser due to a reliance on jquery for plugins or other libraries.

foos = Element.find('.foo')
# => [<div class="foo">, ...]

# => JQuery

foos.on(:click) do
  alert "element was clicked"

Getting Started


opal-jquery is distributed as a gem, and needs to be added to your Gemfile:

# Gemfile
gem 'opal'
gem 'opal-jquery'


opal-jquery can now be easily added to your opal application sources:

# app/application.rb

# Remember to compile opal-jquery with your javascript application.
# See "Compiling" below for an example on compiling dependencies.
require 'opal/jquery'

alert "Hello from jquery + opal"

The #alert method is provided by opal-jquery. If the message displays, then jquery support should be working.


When compiling your application to javascript, you must be sure to include both Opal and Opal-JQuery so they'll be available to your application:

require 'opal'
require 'opal-jquery'

builder = Opal::Builder.new

File.binwrite('application.js', builder.to_s) # must use binary mode for writing

then simply load the compiled file in your html:

<!DOCTYPE html>
    <script src='https://code.jquery.com/jquery-3.3.1.min.js' integrity='sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=' crossorigin='anonymous'></script>
    <script type='text/javascript' src='./application.js'></script>

opal-jquery expects a jquery library to be loaded. This example loads it remotely from jquery.com, but a locally downloaded copy works just as well, or- if you're using rails- jquery may be included automatically.

This example builds opal, opal-jquery and the application into a single .js file, but you may build them separately, if you so choose. Just remember to include each respective script in your html!

How does opal-jquery work

opal-jquery provides an Element class, whose instances are toll-free bridged instances of jquery objects. Just like ruby arrays are just javascript arrays, Element instances are just jquery objects. This makes interaction with jquery plugins much easier.

Interacting with the DOM

Finding Elements

opal-jquery provides the Element class, which can be used to find elements in the current document:


Element.find is aliased to Element[]:


These methods acts just like $('selector'), and can use any jQuery compatible selector:

Element.find('#navigation li:last')

The result is just a jQuery instance, which is toll-free bridged to instances of the Element class in ruby:

# => Element

Instances of Element also have the #find method available for finding elements within the scope of each DOM node represented by the instance:

el = Element.find('#header')
el.find '.foo'
# => #<Element .... >

Running code on document ready

Just like jQuery, opal-jquery requires the document to be ready to be able to fully interact with the page. Any top level access should use the ready? method:

Document.ready? do
  alert "document is ready to go!"

The Kernel#alert method is shown above too.

Event handling

The Element#on method is used to attach event handlers to elements:

Element.find('#header').on :click do
  puts "The header was clicked!"

Selectors can also be passed as a second argument to handle events on certain children:

Element.find('#header').on(:click, '.foo') do
  puts "An element with a 'foo' class was clicked"

An Event instance is optionally passed to block handlers as well, which is toll-free bridged to jquery events:

Element.find('#my_link').on(:click) do |evt|
  puts "stopped the event!"

You can access the element which triggered the event by #current_target.

Document.on :click do |evt|
  puts "clicked on: #{evt.current_target}"

CSS styles and classnames

The various jQuery methods are available on Element instances:

foo = Element.find('.foo')

foo.add_class 'blue'
foo.remove_class 'foo'
foo.toggle_class 'selected'

There are also added convenience methods for opal-jquery:

foo = Element.find('#header')

# => 'red lorry'

foo.class_name = 'yellow house'

# => 'yellow house'

Element#css also exists for getting/setting css styles:

el = Element.find('#container')
el.css 'color', 'blue'
el.css 'color'
# => 'blue'

HTTP/AJAX requests

jQuery's Ajax implementation is also wrapped in the top level HTTP class.

HTTP.get("/users/1.json") do |response|
  puts response.body
  # => "{\"name\": \"Adam Beynon\"}"

The block passed to this method is used as the handler when the request succeeds, as well as when it fails. To determine whether the request was successful, use the ok? method:

HTTP.get("/users/2.json") do |response|
  if response.ok?
    alert "successful!"
    alert "request failed :("

It is also possible to use a different handler for each case:

request = HTTP.get("/users/3.json")

request.callback {
  puts "Request worked!"

request.errback {
  puts "Request didn't work :("

The request is actually triggered inside the HTTP.get method, but due to the async nature of the request, the callback and errback handlers can be added anytime before the request returns.

Handling responses

Web apps deal with JSON responses quite frequently, so there is a useful #json helper method to get the JSON content from a request:

HTTP.get("/users.json") do |response|
  puts response.body
  puts response.json

# => "[{\"name\": \"Adam\"},{\"name\": \"Ben\"}]"
# => [{"name" => "Adam"}, {"name" => "Ben"}]

The #body method will always return the raw response string.

If an error is encountered, then the #status_code method will hold the specific error code from the underlying request:

request = HTTP.get("/users/3.json")

request.callback { puts "it worked!" }

request.errback { |response|
  puts "failed with status #{response.status_code}"