[FoRK] AJAX: Asynchronous JavaScript + XML

Ken Meltsner meltsner at gmail.com
Wed Mar 30 11:46:53 PST 2005


AJAX uses IE's XMLHTTPRequest object (or its equivalent in Firefox,
etc.) to perform synchronous or asynchronous HTTP GETs or POSTs.

IIRC, KnowNow/modpubsub uses an older trick to keep an HTTP request
open for additional data.  Other tricks include the use of an
invisible frame or iframe to retrieve content without the user
noticing.

Two things have changed to make AJAX feasible in relatively recent times:

*  IE 6 has become quite common, and it includes the XMLHTTPRequest
object by default -- older versions of IE would only have it if the MS
XML parser DLL had been installed.

*  The non-IE browsers picked a syntax and made sure that they had a
comparable object available as well.

There have been other changes that have benefited AJAX-style interfaces:

*  Java applets became viewed as a hellish mess of incompatibilities
and bloat rather than the solution for all user/server interaction
issues

*  Javascript has become much more stable (and I believe, faster).

*  A number of kickass Javascript coders have made compelling use of
the AJAX style.

So, it's been the usual situation:

*  Availability of an acceptable least-common denominator capability

*  Alternatives are perceived as being quicksand traps

*  Applications actually work better with the new capability than without

AJAX and XHR have been used for several years, in fact, but it took
GMail and similar apps to get people to notice that there was
something novel about it.

Ken


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