JS hex/ascii

hex2ascii2hex.js

//Thanks stackoverflow
//http://stackoverflow.com/questions/3745666/how-to-convert-from-hex-to-ascii-in-javascript

function a2hex(str) {
  var arr = [];
  for (var i = 0, l = str.length; i < l; i ++) {
    var hex = Number(str.charCodeAt(i)).toString(16);
    arr.push(hex);
  }
  return arr.join('');
}

function hex2a(hexx) {
    var hex = hexx.toString();//force conversion
    var str = '';
    for (var i = 0; i < hex.length; i += 2)
        str += String.fromCharCode(parseInt(hex.substr(i, 2), 16));
    return str;
}

How do you convert (or what do you enter) in hex2a() to convert a hex values such as \u0153
Can it convert these higher hex values?
Thanks