Check the file type!

Old thread, but replying as this was the top result on google for me, so may prove useful to others. SuperMerlin's script works perfectly but is extremely slow on a larger PSB (4-5s for me). Pulling just the format instead of the whole document descriptor sped it up quite a bit:

function getFileFormatFast () {
    var s2t = stringIDToTypeID, c2t = charIDToTypeID;
    try {
        var ref = new ActionReference();
        // Ask ONLY for the 'format' property of the target document
        ref.putProperty(s2t('property'), s2t('format'));
        ref.putEnumerated(c2t('Dcmn'), s2t('ordinal'), s2t('targetEnum'));

        var desc = executeActionGet(ref);
        return desc.hasKey(s2t('format')) ? desc.getString(s2t('format')) : 'Unsaved File';
    } catch (e) {
        return 'Unsaved File';
    }
}

Hi Kukurykus , sorry for the late reply, the SuperMerlin script works perfectly regardless of where the document originated. yet I am grateful for your help. Thank you.

Great job SuperMerlin! That's what I'm looking for. Thank you.

Kukurykus thanks for listening.

activeDocument.name.split(/\./)[1]

or for many dots:

activeDocument.name.match(/[^.]+$/)[0]