More on official documentation

for IE, try:
http://msdn.microsoft.com/workshop and http://msdn.microsoft.com/scripting

for NS try:
http://devedge.netscape.com

for standard specifications try:
http://www.w3.org/ and
http://www.ecma.ch/

for a convenient cross-browser reference try:
http://www.devguru.com/Technologies/ecmascript/quickref/javascript_intro.html

ummmm, for opera try:
http://www.opera.com/opera5/specs.html#ecmascript

for webtv try:
http://developer.webtv.net/authoring/javascript/javascript.htm

if anybody knows of any other frequently used browsers with js support, please email them to me.