... wherein I bloviate discursively

Brian Clapper,

A Case for CoffeeScript in the Browser

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Like many others who do some development for the web, I’ve grown to like CoffeeScript. The CoffeeScript package comes with a Javascript implementation, allowing CoffeeScript to be translated into Javascript directly in the browser. Jeremy Ashkenas, author of CoffeeScript, recommends against using that approach for anything serious, and with good reason. However, there’s one scenario where I find CoffeeScript in the browser to be especially useful.

I sometimes find myself writing new Javascript components, for use in software I’m building. Often these components consist of custom jQuery code that must be tested in the browser. I find it easier to write, test, debug, and demostrate those components in a standalone HTML document. Since I tend to write those components in CoffeeScript lately, I need an easy way to translate the CoffeeScript into Javascript.

Enter coffee-script.js.

Using CoffeeScript in the browser means I don’t require back-end CoffeeScript- to-Javascript translation while working on my code. For example, if I’m putting together a custom jQuery component, it’s easier to code it all in a single HTML document, without relying on a backend framework like Rails to convert the CoffeeScript for me. Using coffee-script.js also means I can package the HTML document and its accompanying images, scripts, and stylesheets, in a Zip file or tarball; I can send that package to someone else, and that person only needs to unpack the package and point a browser at the index.html file to run a demo.

The set up is easy enough. Here’s an example. Suppose I’m building a new jQuery UI component, for use in an application. While building and testing the Javascript, I’ll frame the CoffeeScript in a simple HTML document like this:

CoffeeScript Test File
<title>Widget test</title>
<script type="text/javascript" src=""></script>
<script type="text/javascript" src=""></script>


<script type="text/coffeescript" src=""></script>

<h1 id="header" style="color: red">CoffeeScript test.</h1>

<!-- Pull coffee-script.js in AFTER all the CoffeeScript. -->
<script type="text/javascript" src=""></script>

It’s important that the <script> tag for coffee-script.js occur after the actual CoffeeScript in the document. It will then find any <script> elements with type="text/coffeescript", convert them to Javascript, and run them.

If you prefer, of course, you can download copies of jquery.min.js, jquery.ui.js and coffee-script.js, you can use local copies of the Javascript files that are imported.

You can also put the CoffeeScript directly inline:

Embedded CoffeeScript
<script type="text/coffeescript">
$(document).ready ->
  alert "Better stuff will go here"

I usually keep it in a separate file, though. It’s easier to deploy that way, when I’m done developing and testing it. Also, my editor will highlight the syntax properly, if I store the actual source in a .coffee file.

For performance reasons, you don’t want to deploy your code with CoffeeScript in the browser. But, during development and testing, this technique can be a useful timesaver.