"A recent project has me working closely with the browser XMLHttpRequest object. Like any good little dev., I've been writing tests for various Ajax routines. These test are simple .htm files run from a local directory on my computer—they do not reside on an HTTP server. Consequently, after an XMLHttpRequest has its send() fired, no actual HTTP request is made. Instead, the browser simply accesses the file on the harddrive via I/O operations—not the HTTP protocol. During my testing experience with a local setup, I've noticed a few quirks that deserve attention. If you're a developer also debugging in a disconnected environment, you may find these notes useful."