JavaScript versions: is it worth learning all of them?

OK, there appear to be three major Document Object Models for
DHTML and JavaScript,
document.layers -- Netscape
document.all -- Micro$oft
document.GetElementById -- W3C (used by Firefox, etc.)

Trying to find information on the document.layers model, I continuously
get directed to one or another page:
http://developer.netscape.com/
which has stopped responding to http queries some time ago. (Lynx just
times out trying to connect.)

Micro$oft's site either has no downloadable references or they make them
very hard to find. Instead, it is necessary to navigate through a maze of
pages, one for each object, method, function, style, property, keyword or
whatever that they support with their version of JavaScript -- thousands
and thousands and thousands of tiny little pages.

Finding JavaScript references that don't refer only to Netscape's and/or
Micro$oft's implementations was a bit difficult but I eventually did find
it W3C's DOM in downloadable format and have used the information in that
to create JavaScript versions of the sliding-block puzzles[1] I designed.

I thought it would be nice to support *all* browsers but then have
learned from several sources that Netscape's new browser version
is selectable to emulate Firefox or IE. No mention is made of it
supporting the old Netscape standard. Then I found out in a newsgroup
for the handicapped that Internet Explorer version 6 now supports the
document.GetElementById model and that my puzzles work with IE 6.

That suggests that it may be pointless to bother learning anything but
the W3C DOM.

So, should I bother at all to try to learn the document.layers and
document.all methods of implementing DHTML or will the W3C DOM become
supported enough that the other models become superfluous?


[1] http://www.chebucto.ns.ca/~af380/JSNSPuz.html
http://www.chebucto.ns.ca/~af380/MHPuzzle.html
http://www.chebucto.ns.ca/~af380/AMPuzzle.html
--
Norman De Forest http://www.chebucto.ns.ca/~af380/Profile.html
af380@chebucto.ns.ca [=||=] (A Speech Friendly Site)
Q. Which is the greater problem in the world today, ignorance or apathy?
A. I don't know and I couldn't care less.