Today I did some experimenting with the caching of downloaded code (or On-Demand Javascript, whatever you want to call it).
I’ve set up a small testing suite that currently tests 3 different ways of downloading code: script-tag insertion via DOM, XmlHttpRequest as a GET and XHR as a POST.
These are my results for now:
Method | IE6 | Firefox 1.07 | Firefox 1.5b2 | Safari 2.0 | Opera 8.5 |
---|---|---|---|---|---|
script_dom | cached | cached | cached | cached | cached |
xhr_post | not cached | not cached | not cached | not cached | not cached |
xhr_get | cached | not cached | cached | not cached | not cached |
(Results are the same for Win and OS X where both browsers are available (FF & Opera))
This gives an interesting picture: Firefox does not seem to cache any scripts, neither the ones loaded via DOM nor those loaded via XHR. Only IE loads an XHR GET request from cache.
I’ve got the script in my public testing area, so you can test it for your own browser. Please do so and correct my values if you receive different results.
The sources of my tests are available, too: index.phps and js.phps. I did my testings using the latest prototype.js library. Maybe I will try it later on with another library (e.g. with dojo.io.bind).
I’d be interested in more ways to download code (especially via document.write since I haven’t been able to include this properly to my tests) and in your results for other browsers. Just leave a comment.
UPDATE: I have now included the Expires
header field with the Javascript file. Now FireFox in both version caches the script with script_dom, in version 1.5b2 it also caches XHR with GET requests.