code: public ApplicationResource addJsUrl(final String url) {
  		if (Util.empty(url)) {
  			throw new IllegalArgumentException("A URL must be provided.");
  		}
  		ApplicationResource res = new ApplicationResource(url);
  		addJsResource(res);
  		return res;
  	}
docs: Add custom javaScript located at the specified URL to be used by the Application.
  
  @param url URL to a javaScript resource
  @return the application resource in which the URL details are held