string to hex string /hex string to string conversion

The Quectel BC95 module expects the data payload as hex strings. Are the following methods, the most memory efficient way of doing this?

//convert to a hex string
    for (var i = 0; i < data.length; i++) {
      var s = data.charCodeAt(i).toString(16);
      while (s.length < 2) {
        s = '0' + s;
      }
      msg += s;
    }

and conversely:

for (let ndx = 0; ndx < (recvData[1] * 2); ndx += 2) {
    let i = parseInt("0x" + recvData[2].substring(ndx, ndx + 2)); //ascii hex to integer
    sockData[connection] += String.fromCharCode(i);          //build a string
  }

From my limited understanding, this code would create a string, append and create a new string, rinse and repeat. This seems like a bit of overhead. I did consider typed arrays, but how do I convert these back to a string in one go?