There are some errors in the code of module SX127x

In SX.prototype.setTxConfig

SX.prototype.setTxConfig = function( options ) {
  options = this.commonSetConfig(options);
  ....
  this.w( REG.PREAMBLEMSB, ( preambleLen >> 8 ) & 0x00FF );
  this.w( REG.PREAMBLELSB, preambleLen & 0xFF );
};

missing "options." before "preambleLen"