1. A method of loading source files, comprising: receiving, in the course of executing a script, an indication that a source file on which a current class or function depends is not available, wherein the current class or function is called or executed during the execution of the script; and continuing execution of remaining portions of the script, if any, that do not depend on the source file, or continuing on to other processing tasks if no such portions remain, while the source file is loaded asynchronously.