JavaScript is of course standardized. What confuses many is that it's a scripting language, so interacts with the underlying DOM, and that each doctype has its own DOM. Morever, JavaScript is used with other, non-HTML DOMs as well, such as Acrobat. However, the language itself is standardized.
ah, you got me there, but the ramifactions are a consideration; however small.
it's not just doctype aswell, different browsers need to be considered regardless of doctype.. non-browser-dependant js code is usually quite messy looking at the very least.
for me it's a very small consideration; because i minimize the importance of js code

if i scripted a site entirely in js, it would be a bigger consideration, as some people are absolutely nuerotic about their security online, and disabling js isn't difficult.
admittadly though, it isn't as likely as someone not having flash installed/enabled, or not having an up-to-date version of java.
there has never been a situation where we had to code around a "non-JavaScript" user. Not once.
not to deliberately perpetuate the, already well-perpetuated js-fear.. but you wouldn't neccessarily know the amount of non-js user's who couldn't use your company/ies, or client(s) sites if elements of those sites were totally js dependant.
for the most part, users go elsewhere when things don't work as expected, regardless of whether the problem's on a page, or with a security setting.. and almost anything that's functionally js-dependant doesn't need to be..
to me, that seems to need zero-consideration as to how to do something that may be important to standard flow, such as setting a hyperlink on something.
edit: although, that zero consideration ends up causing stoopidly large considerations sometimes; made annoying by the fact that one embedded line of JS would solve an otherwise difficult problem instantly and cleanly.