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Scope your OOP Coffeescript in modern Rails Apps

This post shows you how to easily integrate and scope your frontend Javascript. Keep your legacy code and rebuild your app step by step.

Let’s build an async json loaded component (Ajax), without using jQuery at all, which is used to render a chart.

Code on GitHub

What you will learn

  1. build reusable components
  2. split data, rendering and logic (without using a Framework)


Simply think of a namespace and add it as a class to your class, in our case this would be the class coffeecomponent-component-name. -component-name building the scope.

Add component div-wrapper to your HTML5 view

In your rails view, where you want to display data, add this div:

<!-- in app/views/welcome/index.html.erb -->
<div class="coffeecomponent-nameboard" data-url="<%= api_names_path %>">
  <!-- Content gets rendered here -->

use namespaces in your coffeescript

# wrap classes, group classes
window.CoffeeComponent or= {}
# by using `window` in combination with `or= {}`
# each object is instantiated only once
# further objects can then be added by writing
# or adding objects like this:
CoffeeComponent.ThisAbcComponent = class ThisAbcComponent

implement a jQuery independet $(document).ready()

window.CoffeeComponent or= {}
CoffeeComponent.Document = class Document
  ready: (fn = null) ->
    if document.attachEvent?
      if document.readyState is "complete" or document.readyState is not "loading"
        fn() if fn?
      document.addEventListener 'DOMContentLoaded', ->
        fn() if fn?

implement a jQuery independet Ajax Json Getter

window.CoffeeComponent or= {}
CoffeeComponent.AsyncJsonGet = class AsyncJsonGet
  constructor: (@url, @fn = null) ->
    @request = new XMLHttpRequest()
    @request.open('GET', @url, true)
    @request.onload = =>
      if @request.status >= 200 and @request.status < 400
        # Success!
        data = JSON.parse(@request.responseText)
        if @fn? then @fn(data) else data
        # reached server, but it returned an error
    @request.onerror = ->
      # error

write the component itself

window.CoffeeComponent or= {}
CoffeeComponent.Nameboard = class Nameboard
  constructor: (@data, @target) ->
    elem = document.querySelector(@target)
    elem.innerHTML = "<ul>"
    for name in @data
      elem.innerHTML += "<li>Hello #{name}!</li>"
    elem.innerHTML += "</ul>"

hook up your component in its controller’s js asset file

# app/assets/javascript/welcomes.js.coffee
new CoffeeComponent.Document().ready ->
  do -> # each component instantiation in a self executing function
    renderNameboard = '.coffeecomponent-nameboard'
    element = document.querySelector(renderNameboard)
    return unless element?
    url = element.dataset.url
    new CoffeeComponent.AsyncJsonGet url, (data) ->
      new CoffeeComponent.Nameboard(data, renderNameboard)


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