hextouint8a

function hextouint8a(hexString) {
  if (hexString.length % 2 != 0)
    throw "Invalid hexString";
  var arrayBuffer = new Uint8Array(hexString.length / 2);

  for (var i = 0; i < hexString.length; i += 2) {
    var byteValue = parseInt(hexString.substr(i, 2), 16);
    if (byteValue == NaN)
      throw "Invalid hexString";
    arrayBuffer[i/2] = byteValue;
  }
  return arrayBuffer;
}