Byte array to Hex string conversion in javascript

Question

I have a byte array of the form [4,-101,122,-41,-30,23,-28,3,..] which I want to convert in the form 6d69f597b217fa333246c2c8 I\'m using below func

Answer 1

Since this is the first Google hit for "js byte to hex" and I needed some time to understand the function of Bergi, I rewrote the function and added some comments that made it easier for me to understand:

function byteToHex(byte) {
  // convert the possibly signed byte (-128 to 127) to an unsigned byte (0 to 255).
  // if you know, that you only deal with unsigned bytes (Uint8Array), you can omit this line
  const unsignedByte = byte & 0xff;

  // If the number can be represented with only 4 bits (0-15), 
  // the hexadecimal representation of this number is only one char (0-9, a-f). 
  if (unsignedByte < 16) {
    return '0' + unsignedByte.toString(16);
  } else {
    return unsignedByte.toString(16);
  }
}

// bytes is an typed array (Int8Array or Uint8Array)
function toHexString(bytes) {
  // Since the .map() method is not available for typed arrays, 
  // we will convert the typed array to an array using Array.from().
  return Array.from(bytes)
    .map(byte => byteToHex(byte))
    .join('');
}

• For more information about the const unsignedByte = byte & 0xff-part, check What does AND 0xFF do?.
• Array.from is not available in every browser (e.g. not in IE11), check How to convert a JavaScript Typed Array into a JavaScript Array for more information

The OP forgot to add the leading 0 for numbers that can be displayed with only 4 bits.