I recently gave a talk on Building progressive UIs with Grails at gr8conf in Copenhagen and was really pleased with the feedback & comments I received afterwards. There was a question asked at the end that I felt in retrospect I could have answered better, though. I had mentioned that the Grails AJAX tags were something that should be avoided as they write script blocks directly into the page and event handlers directly onto HTML elements. I was pitching an approach based on a clean separation of clean semantic markup and script enhancements and inline script violates that separation.
The resources plugin’s
r:use tag doesn’t write out anything directly to the page but rather adds a resource module to a list that will get written out at the appropriate place in the page when the
r:use. In a complex app this can be a real boon as it might not be obvious from the top level GSP exactly which modules are going to get rendered. Also if a module is later added to or removed from a page you don’t need to worry about fiddling around with resource declarations in the top level GSP. Taglibs or templates become real drop in components whilst maintaining a nice clean separation of markup and script. Even better, if you use the same resource dependency multiple times the plugin ensures the resources are actually only linked once.
r:layoutResources is typically used in a SiteMesh layout the resources your module depends on can even be ones that need to appear in the
head of the document. The SiteMesh is rendered after the GSP it decorates so any
r:use calls will already have been made.