Javascript ArrayBuffer to Hex

by 
function buf2hex(buffer) { // buffer is an ArrayBuffer
  return [...new Uint8Array(buffer)]
      .map(x => x.toString(16).padStart(2, '0'))
      .join('');
}

// EXAMPLE:
const buffer = new Uint8Array([ 4, 8, 12, 16 ]).buffer;
console.log(buf2hex(buffer)); // = 04080c10

This function works in four steps:

  1. Converts the buffer into an array.
  2. For each x the array, it converts that element to a hex string (e.g., 12 becomes c).
  3. Then it takes that hex string and left pads it with zeros (e.g., c becomes 0c).
  4. Finally, it takes all of the hex values and joins them into a single string.

Below is another longer implementation that is a little easier to understand, but essentially does the same thing:

function buf2hex(buffer) { // buffer is an ArrayBuffer
  // create a byte array (Uint8Array) that we can use to read the array buffer
  const byteArray = new Uint8Array(buffer);
  
  // for each element, we want to get its two-digit hexadecimal representation
  const hexParts = [];
  for(let i = 0; i < byteArray.length; i++) {
    // convert value to hexadecimal
    const hex = byteArray[i].toString(16);
    
    // pad with zeros to length 2
    const paddedHex = ('00' + hex).slice(-2);
    
    // push to array
    hexParts.push(paddedHex);
  }
  
  // join all the hex values of the elements into a single string
  return hexParts.join('');
}

// EXAMPLE:
const buffer = new Uint8Array([ 4, 8, 12, 16 ]).buffer;
console.log(buf2hex(buffer)); // = 04080c10

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