creditor_reference.js

function generate_creditor_reference( ref ) {
  if ( /^[A-Za-z0-9]{0,21}$/.test( ref ) ) {

    ref = ref.toUpperCase();

    let cr = '';
    for ( let i = 0; i < ref.length; i++ ) {
      let cc = ref.charCodeAt(i);
      if ( 65 > cc ) {
        cr += cc - 48;
      } else {
        cr += cc - 55;
      }
    }
    cr += '271500';

    while ( cr.length > 10 ) {
      cr = ( cr.substring( 0, 10 ) % 97 ) + cr.substring( 10 );//concat
    }

    return 'RF' + ( 98 - cr % 97 + '' ).padStart( 2, '0' ) + ref;
  }
}


function check_creditor_reference( ref ) {
  if ( /^RF\d{2}[A-Za-z0-9]{0,21}$/.test( ref ) ) {

    ref = ref.toUpperCase();
    ref = ref.substring( 4 ) + ref.substring( 0, 4 );

    let cr = '';
    for ( let i = 0; i < ref.length; i++ ) {
      let cc = ref.charCodeAt(i);
      if ( 65 > cc ) {
        cr += cc - 48;
      } else {
        cr += cc - 55;
      }
    }

    while ( cr.length > 10 ) {
      cr = ( cr.substring( 0, 10 ) % 97 ) + cr.substring( 10 );//concat
    }

    if ( 1 == cr % 97 ) {
      return true;
    }

  }
  return false;
}