JavaScript Caching: appendChild vs document.write

I found myself trying to prefetch some data which would appear in an iframe. I wanted to see if requesting the same JSON in the parent page and then in the iframe would cause the second request, made in the iframe, to hit the browser's cache in all cases. It turns out that for Internet Explorer and Web Kit based browsers it depends on how you request the JSON in the parent page.

If you use appendChild in IE the identical JS request will hit the browser cache.
If you use document.write in IE it will not hit the cache.

However, in Chrome and Safari if you appendChild in the parent, you will miss the cache. Using document.write in the parent page causes a cache hit.

Here are the results I gathered.

Cache Hit?	both document.write	parent document.write iframe appendChild	parent appendChild iframe document.write	both appendChild
Internet Explorer	miss	miss	hit	hit
Firefox	hit	hit	hit	hit
Chrome	hit	hit	miss	miss
Safari	hit	hit	miss	miss
Opera	hit	hit	hit	hit
Android	?	?	?	?
iOS	?	?	?	?

All versions of IE behaved the same, I didn't check different versions of the other browsers.

To test this I wrote a test web application called json-caching-exploration. It's a simple web app that runs on App Engine.

Server and HTML
JavaScript

I haven't run this against mobile browsers yet. If you give it a try please let me know what you find.

It's a shame that these browsers behave differently, especially given the differences in browser behavior between loading JavaScript using document.write and appendChild.

Opera on the XO Laptop

No I'm not talking about singing.

I was looking forward to the release of Firefox 3 with great anticipation. I had tried out the beta versions and noticed the improvements in JavaScript execution speed and memory footprint. Since the XO laptop is relatively slow and memory constrained compared to many of the other computers that I work with, I was really hoping that Firefox 3 would be a big improvement over Firefox 2. It turns out, for the XO, it wasn't. The place where the limitations were most apparent, was scrolling on a large web page. The page would hang for a second or so and then slowly creep down. It probably had to do with the short supply of available RAM on my happy little green machine.

As momentum was building for Firefox 3, I started to hear good things about Opera 9.51. When I ran into performance issues on Firefox and the XO, I decided to give Opera a try. Some thought I was crazy since, as Arne mentioned, the XO can be a bit slow. Yes, the XO laptop is a different environment than most other computers out there, and Opera has turned out to be an improvement.

To set up Opera on the XO, I began by downloading from the Opera web site. I selected Opera 9.51 for Linux i386, selected RedHat as the distribution in the drop down menu, then I selected RedHat 6.2, 7.1, 7.2, 7.3, 8.0, 9 and checked the box to Download this package in TAR.GZ format. Whew.



Next, unpack the archive using

tar zxvf opera-9.51.gcc4-static-qt3.i386.tar.gz

and then run

install.sh -s

From there, you can just type opera on the command line in the terminal to start it up.

Firefox 3 Beta 2

I recently downloaded the second beta of Firefox 3 from Portable Apps. I didn't want to replace the version of Firefox I already had installed, so I used the version from Portable Apps which runs as a standalone binary. Sometimes it's really nice to unpack a program without touching the registry or worrying about installing.

Overall, I'm very happy with the changes I've seen in the latest version. I had heard that there have been some improvements to the JavaScript engine in this version, and they are noticeable. When I logged in to gmail it seemed a bit more responsive. I have to say though that my favorite changes are in the address bar. When typing the address, the address bar shows addresses, titles, and logos for pages that you've already visited. Firefox 2 did this too, but I think 3 gives more detail and a larger number of results. I found myself using it much more often than in 2. Part of the reason is that it shows the most recently visited page at the top instead of the shortest match. I also liked that you could star a URL to add it to your bookmarks, and you can even select a folder and tag the URL from within the address bar.