Hex string to byte and other way round conversion functions.

hexstring.js

function byteToHexString(uint8arr) {
  if (!uint8arr) {
    return '';
  }
  
  var hexStr = '';
  for (var i = 0; i < uint8arr.length; i++) {
    var hex = (uint8arr[i] & 0xff).toString(16);
    hex = (hex.length === 1) ? '0' + hex : hex;
    hexStr += hex;
  }
  
  return hexStr.toUpperCase();
}

function hexStringToByte(str) {
  if (!str) {
    return new Uint8Array();
  }
  
  var a = [];
  for (var i = 0, len = str.length; i < len; i+=2) {
    a.push(parseInt(str.substr(i,2),16));
  }
  
  return new Uint8Array(a);
}