If I have a link like this:
var a = $("[data-btn='login']"); //This?
var a = $("[data-btn=login]"); //Or this?
As of jQuery 1.5, both
" quotes will work, and function identically.
jQuery used to require quotes around attribute values, so your second selector won't work with previous versions. If you're stuck with an older version for some reason, use the first selector.