scriptxduplex.js

// Whether duplex is supported can be checked in one of two ways:
// These rely on the driver correctly reporting that it doesnt support duplex.

// 1. catch the error that occurs when trying to set duplex
try { 
  factory.printing.duplex = 2;
} catch (e) {
  // duplex isnt supported, will need to be manual
}

// 2. use duplex2. 0 is returned if not supported
// (http://scriptx.meadroid.com/knowledge-bank/technical-reference/printing-factoryprinting/duplex2.aspx)
if ( !factory.printing.duplex2 ) {
    // duplex isnt supported, will need to be manual
}