When working with a DOM (Document Object Model, basically an XML tree), .value refers to the value of an XML node. So:
Blah Blah
In this case if you wanted to reference "Blah Blah" it would be SomeNode.value.
FormCalc has more direct access to the DOM, so if you don't add the .value to the end it's smart enough to figure out that that's what you want (but you can still specify it explicitly if you want). JavaScript doesn't have that advantage so you must specify .value.
So, in FormCalc:
SomeNode == SomeNode.value == "Blah Blah"
whereas, in JavaScript:
SomeNode == [an XFA object] (not a specific value)
SomeNode.value == "Blah Blah"
Hope that helps explain it a bit.
Chris
Adobe Enterprise Developer Support