Why it’s useless in real applications?
Finally, JavaScript doesn’t have any multithreading capabilities, except whatever comes implicitly
from the web browser’s internal use of threads.
Another reference: Multi-threading in JavaScript
Only thing what javascript (thus AJAX) is currently capable of, is to imitate multithreading, which is 100% different thing than actual multithreading.
So there we go, stated in plain english. Javascript as an language (& infastructure) is lcking a lot. So it definitely very limited platform, and not ”the ultimate language” (like sadly every now and then people foolishly believe).
Update 30.8.2009
Yes, some improvements are coming, but it still takes some time for this feature to be universally available. Which comes into one primary curse of javascript, namely various mismatches javascript implementations in different browsers. Saying that framework libraries take care of such is then again problematic statement, since due to language structure, different libraries can very easily conflict with each other. Also frameworks simply can’t make unsupported things to magically work.
One company now betting into javascript is Palm with its’ new Palm Pre phone, which is purely based into javascript based applications. And there comes the problem, after coolness factor of this approach wears out, problems arise. Reading development forums for Pre reveals that there is various problems, which appear to come from the usage of javascript, and its’ slow performance compared to rivals like iPhone (with Objective C based apps).