Autoit how to implement javascript functions?

Hello coders. I've been working with the FF.au3 extension which allows user to do things in Firefox via javascript (_FFCmd function sends javascript and then returns values)

But in a lot of cases, there may come handy a javascript function, and now I found that it is probably essential to implement one. The case is:

http://stackoverflow.com/questions/15055185/document-getelementsbyclassname-exact-match-to-class

I've got elements with class "item" and class "item one"
if I do

_FFCmd("someMoreThings.getElementsByClassName('item')")

, it picks the items "item one" also. I need to pick only "item". That issue is solved by a javascript/jquery function on stackoverflow forum. How can I do something like that in AutoIt?

Thanks for help, Knuckles

EDIT: I'm thinking of using something like this:

document.getElementsByClassName('item' && !'item one');

JSLint says Weird condition. (so it's probably not the right way to do it)