code: public ApplicationResource addJsFile(final String fileName) {
  		if (Util.empty(fileName)) {
  			throw new IllegalArgumentException("A file name must be provided.");
  		}
  		InternalResource resource = new InternalResource(fileName, fileName);
  		ApplicationResource res = new ApplicationResource(resource);
  		addJsResource(res);
  		return res;
  	}
docs: Add custom JavaScript held as an internal resource to be used by the application.
  
  @param fileName the JavaScript file name
  @return the application resource in which the resource details are held