If you are developing a web application using Jetty via Eclipse, by default, changes made to static resources such as external JavaScript and CSS files are not picked-up on the fly by the running Jetty server. Out of the box, picking up such changes requires that Jetty be stopped and restarted, possibly with the webapp being redeployed in between. In order to enable hot deployment of such resources, modify the [JETTY_ROOT]/etc/webdefault.xml file like so:

<init-param>
    <param-name>maxCachedFiles</param-name>
    <param-value>0</param-value>
</init-param>

By way of colleague and friend, Justin Alpino.