Better code downloading with AJAX

I’ve been playing with Code downloading (or Javascript on Demand) a little more.

Michael Mahemoff pointed me at his great Ajaxpatterns in which he suggests a different solution:

if (self.uploadMessages) { // Already exists
return;
}
var head = document.getElementsByTagName("head")[0];
var script = document.createElement('script');
script.type = 'text/javascript';
script.src = "upload.js";
head.appendChild(script);

Via DOM manipulation a new script tag is added to our document, loading the new script via the ‘src’ attribute. I have put a working example here. As you can see this does not even need to do an XmlHttpRequest (XHR later on) so it will also work on browsers not supporting that.

So why use this approach and not mine? Initially I thought that it was not as good as doing it via XHR because you receive a direct feedback (i.e. a function call) when the script has been loaded. This is per se not possible with this technique. But as in good ol’ times a simple function call at the end of the script file will do the same job (compare source codes from the last example and this one (plus load.js)).

Using this method to load code later on also provides another “feature” (thanks for that hint to Erik Arvidsson): Unlike XHRs Firefox also provides a cache for scripts loaded that way. There seems to be a disagreement about whether this is a bug or a feature (people complaining that IE caches such requests while it could be quite useful in this scenario).

When using dynamically generated javascript code you will also have to keep your HTTP headers in mind (scripts don’t send them by default). The headers Cache-Control and Last-Modified will do usually (see section 6.1.2 of my thesis)

The method above is also the method used by Dojo, a developer (David Schontzler) commented, too. He says that Dojo also only loads the stuff the programmer needs, so little overhead can be expected from this project.

Also Alex Russell from Dojo left a comment about bloated javascript libraries. He has some good points about script size to say (read for yourself), I just want quote the best point of his posting:

So yes, large libraries are a problem, but developers need some of the capabilities they provide. The best libraries, though, should make you only pay for what you use. Hopefully Dojo and JSAN will make this the defacto way of doing things.

So hang on for Dojo, they seem to be on a good way (coverage of Dojo to follow).

Finally I want to thank you all for your great and insightful comments!

ajax, dojo, code downloading, javascript on demand, caching, http headers

No Google Office To Be Expected

According to an interview of Sergey Brin (founder of Google) by John Battelle, Google does not plan to publish a web based office, as rumored before (fueled by a new partnership between Google and Sun (owner of openoffice.org)).

“I don’t really think that the thing is to take a previous generation of technology and port them directly,” he said. I agree with that. We have to think about new tools to be our future web apps. Just porting office apps to the web won’t work.

So what’s this deal about now? Google seems to want a wider distribution of their toolbar. According to the Cnet coverage (via John Battelle again):

“Details about what exactly that will entail were vague at best, with the only nugget offered being that Sun, in the immediate future, will make Google’s toolbar a standard part of the package when users download Sun’s Java Runtime Environment from the server seller’s Web site.”

Sergey Brin further stated that distributed thin web applications allowed you to do “new and better things than the Office package and more.” So further tools by Google can be expected.

google, office, sun, openoffice, ajax