A system and method provides secondary resource files in response to a request for a web page from a client device. In response to the request, a server provides an HTML file which identifies a secondary resource file, such as a javascript file, and the current version value of the secondary resource. The HTML file may be associated with a header which prevents the file from being cached. If there is no locally-cached version of the secondary resource file, the file is requested from the server. The server will transmit the secondary resource file with a header indicating that the file is to be stored indefinitely. If there is a locally-cached version of the secondary resource file, the client device compares the version value of the locally-cached version to the received current version value. If the values are different, the client requests the differences between the files. The server provides a difference file which the client device uses in conjunction with the locally-cached version of the secondary resource to generate the current version of the secondary resource.