How to failover to a local file if a CDN fails with RequireJS

by David Burgos

To use a CDN is recommended for speed and a better performance but for example, what happens if a CDN fails or you want to enable offline mode?

If you are using RequireJS there is a way to do this, let’s see a simple example.

Failover system

Just add another route to the same object

requirejs.config({ 
  enforceDefine: true, 
  paths: { 
    jquery: [ 
      '//ajax.aspnetcdn.com/ajax/jquery/jquery-2.0.0.min', 
      'js/jquery-2.0.0.min' 
    ] 
  } 
});

So if the first route fails, RequireJS will try to load the second one (and so on…).

Using it

There is no change about handling the variables

require(['jquery'], function($) { 
  // Use $ normally... 
});

Read more about config fallbacks
More information RequireJS API