Fallback for CDN asset loading

[Karel]

Hi,

What would you think to add a fallback option to javascript_include_tag?

If I load dojo from Google CDN, I'd like a fallback. The easiest way to do so is by putting a script tage right after it:

<script>typeof(dojo) === "undefined" && document.write(unescape('%3Cscript src="assets/javascripts/dojo.js"%3E%3C/script%3E'));</script>

But the dojo library should go in your /vendors/assets/ not in your /public/assets. To get it served, I need to play with the config.assets.precompile if I understand well. Anyway, it all seem very hacky too me.

What would you think of being able to do something like that:

= javascript_include_tag "http://ajax.googleapis.com/ajax/libs/dojo/1.6.1/dojo/dojo.xd.js", :test => 'typeof(dojo) === "undefined"', :local => 'local/path/to/dojo'

That way rails take care of putting the extra <script> tag for us with the test and most importantly, can precompile the file and set the good path. 

What do you think?

[Tim Shaffer]

Why not just something like this? Then you can put your dojo.js in assets/javascripts and compile it like normal. Seems kind of unnecessary to add extra logic to javascript_include_tag

<%= javascript_include_tag "http://ajax.googleapis.com/ajax/libs/dojo/1.6.1/dojo/dojo.xd.js" %>

<script type="text/javascript">

  if ( typeof(dojo) === "undefined" ) { 

    script = document.createElement('script');

    script.type = "text/javascript";

script.src = '<%= asset_path "dojo.js" %>';

document.getElementsByTagName('head')[0].appendChild(script);

  }

</script>

[Karel]

Hi Tim,

That's what I'm doing and it works just fine.

Though the second <script> tag belongs to the first one and could be generated/linked to it.

It is just an idea that would make it cleaner and more self contained.

[Tim Shaffer]

Gotcha. You could always create a helper for it.