Auto-submit form

Is there a way (preferrably using php... but if javascript is necessary and some kind soul knows how I will use it) to have a form auto-submit when a field is 'full'? I want to be able to scan barcodes of a set length and have a form be automatically submitted to store the information in the database when the barcode field is scanned. Since I'm asking potentially off-topic question anyway, how do I make the fields advance without using the tab key when one field is 'full'? For instance, I want to scan a library card barcode, have the focus shift to the piece barcode field, scan the book barcode, then be auto-submitted once the book barcode is scanned. TIA, (V) -=-=-=-=- No testimony is sufficient to establish a miracle unless the testimony be of such a kind that its falsehood would be more miraculous than the fact which it endeavours to establish. - David Hume -=-=-=-=-