Callbacks are getting momentum, not only in ASP.NET
The recent launch of the Google Suggest beta
attracted a lot of attention to XmlHttp callbacks. Such
features where client-side script asks the server for very
focused updates to the page without reposting it entirely
have been possible ever since frames and javascript exist
(I've done a web-based chat application and treeview based
on hidden frame posting more than 4 years ago), but the
XmlHttp APIs
first found in IE 5
and then in
Mozilla, Safari and Opera (without the need to use an ActiveX, which is a
great improvement) have made it a lot easier and a lot less
hacky. There's even an ongoing W3C attempt at standardizing
such APIs (which unfortunately adds a third syntax to the IE
and Mozilla syntaxes).
So everyone is now realizing what potential it holds to make
better web applications. Here's
an interesting blog entry about the Google
implementation.
But even this very nice Google feature has been available
for
ASP.NET
developers under an easy to reuse form for years: check out
this excellent WebControl.
This being said, to my knowledge,
ASP.NET
2.0 remains
the only server-side technology to natively support
callbacks
with ready-to-use server and client-side event-driven APIs.