SG PayNow QR Code Generator Sample

paynow.js

String.prototype.padLeft = function (n, str) {
  if (n < String(this).length) {
    return this.toString();
  }
  else {
    return Array(n - String(this).length + 1).join(str || '0') + this;
  }
}

function crc16(s) {
  var crcTable = [0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5,
    0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b,
    0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
    0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c,
    0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
    0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b,
    0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
    0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
    0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5,
    0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969,
    0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96,
    0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
    0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03,
    0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
    0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6,
    0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a,
    0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb,
    0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1,
    0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c,
    0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2,
    0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb,
    0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447,
    0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
    0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2,
    0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9,
    0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827,
    0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c,
    0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0,
    0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d,
    0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07,
    0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba,
    0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
    0x2e93, 0x3eb2, 0x0ed1, 0x1ef0];

  var crc = 0xFFFF;
  var j, i;

  for (i = 0; i < s.length; i++) {

    c = s.charCodeAt(i);
    if (c > 255) {
      throw new RangeError();
    }
    j = (c ^ (crc >> 8)) & 0xFF;
    crc = crcTable[j] ^ (crc << 8);
  }

  return ((crc ^ 0) & 0xFFFF).toString(16).toUpperCase().padStart(4, '0');
}


function generatePayNowStr( opts ) {

  const p = [
    { id: '00', value: '01' },                    // ID 00: Payload Format Indicator (Fixed to '01')
    { id: '01', value: '12' },                    // ID 01: Point of Initiation Method 11: static, 12: dynamic
    {
      id: '26', value:                            // ID 26: Merchant Account Info Template
        [{ id: '00', value: 'SG.PAYNOW' },
        { id: '01', value: '2' },                 // 0 for mobile, 2 for UEN. 1 is not used.
        { id: '02', value: opts.uen },            // PayNow UEN (Company Unique Entity Number)
        { id: '03', value: opts.editable.toString() },       // 1 = Payment amount is editable, 0 = Not Editable
        { id: '04', value: opts.expiry }]         // Expiry date (YYYYMMDD)
    },
    { id: '52', value: '0000' },                  // ID 52: Merchant Category Code (not used)
    { id: '53', value: '702' },                   // ID 53: Currency. SGD is 702
    { id: '54', value: opts.amount.toString() },  // ID 54: Transaction Amount
    { id: '58', value: 'SG' },                    // ID 58: 2-letter Country Code (SG)
    { id: '59', value: 'COMPANY NAME' },          // ID 59: Company Name
    { id: '60', value: 'Singapore' },             // ID 60: Merchant City
    {
      id: '62', value: [{                         // ID 62: Additional data fields
        id: '01', value: opts.refNumber           // ID 01: Bill Number
      }]
    }
  ]

  let str = p.reduce((final, current) => {
    if (Array.isArray(current.value)) { //nest loop
      current.value = current.value.reduce((f, c) => {
        f += c.id + c.value.length.toString().padLeft(2) + c.value;
        return f
      }, "")
    }
    final += current.id + current.value.length.toString().padLeft(2) + current.value;
    return final
  }, "")

  // Here we add "6304" to the previous string
  // ID 63 (Checksum) 04 (4 characters)
  // Do a CRC16 of the whole string including the "6304"
  // then append it to the end.
  str += '6304' + crc16(str + '6304');

  return str;

}

Hi I like to query about difference between 010211 (static) and 010212 (dynamic). I have added amount and Bill-reference which will be different for different client. No expiration date. I have tried generating a sample QRcode based on static as well as dynamic with other data remaining the same - both can work . Anyone can tell me whether there is any difference between static and dynamic that I may have missed out? Another query: I added a reference under ID62. It is OK. But I find that after it's scanned by bank apps, this field cannot be amended. If I want to allow it to be amended - can it be done? Just want this reference to be default only. Thanks for any answer.

According to the EMV specifications,

Identifies the communication technology (here QR Code) and whether the
data is static or dynamic.

The Point of Initiation Method has a value of "11" for static QR Codes and
a value of "12" for dynamic QR Codes.

The value of "11" is used when the same QR Code is shown for more than
one transaction.

The value of "12" is used when a new QR Code is shown for each
transaction.

ID62 (refNumber) cannot be edited if you provide it.

The intention is to put individualised QRcode on invoices sent to each client. The dynamic sounds like the client can scan/pay only once? But when I tested it - I find that both the static and dynamic QR codes, I can pay twice successfully.

It's probably not implemented by the payment apps, though the setting is there. It's mentioned in the EMV specs, but not in the SG PayNow specs. There might have been a newer specification, but I have not researched this.