ResourceLoader/Developing with ResourceLoader

ResourceLoader aims to support complex client-side software in both production and development environments. These different environments have unique needs, and ResourceLoader is intended to specialize in both. To achieve this, two distinct modes are available: production and development, also known as "debug" mode.

Development mode (debug=false) is designed to make development as easy as possible, prioritizing the ease of identifying and resolving problems with the software over performance. Production mode (debug=false) makes the opposite prioritization, placing a premium value on performance at the cost of ease of development.

It is important to test your code in both development and production modes, but during day-to-day development, most developers will find it beneficial to use development mode most of the time, only validating their code's functionality in production mode before committing their changes.

Switching modes
As with many other of MediaWiki, ResourceLoader is by default set to deliver resources in production mode, but can be configured to deliver them in development mode by default instead.

You may notice that ResourceLoader requests, such as those made to load.php contain a debug parameter. This parameter influences the way the resources are returned in the response in respect to production or development mode. As a convenience, this parameter may also be used within a MediaWiki page request, allowing the default mode set by $wgResourceLoaderDebug to be overridden.

 http://en.wikipedia.org/wiki/Main_Page? debug=true

Breaking cache
When making frequent changes to code and checking them in a browser, the caching mechanisms designed to improve the performance of web-browsing can quickly become inconvenient. When developing on a system which is not making use of a reverse proxy such as Squid or Varnish, you only need to force your browser to bypass it's cache while refreshing. This can be achieved by pressing CTL+F5 in Internet Explorer, or holding the shift key while clicking the browser's refresh button in most other browsers.

If you are developing behind a reverse proxy, you can either changed the values of $wgResourceLoaderMaxage or wait until is fixed.