On the web it's all dynamic; all the code for handling every situation you might encounter comes down to the client when the page loads and you sort out the details at runtime while the user taps their fingers on the table. If there is a large amount of code to fix one specific browser you can break that out and pull it down only for that browser, but the kind of bugs that jQuery works around tend to be of the death-by-a-thousand-little-cuts variety where it just doesn't pay to refactor that way.