Converting a string into binary and back

Question

I got an assignment to convert a given string into binary and back to a string again.

The first part was easy

function stringToBinary(input) {
  var characters = input.split('');

  return characters.map(function(char) {
    return char.charCodeAt(0).toString(2)
  }).join('');
}

alert(stringToBinary('test'))

However I cannot get my head around how to break the resulting string into their bytes. I tried this so far:

function binaryToString(input) {
  var bits = input.split('');
  
  var byte = '';
  return bits.map(function(bit) {
    byte = byte + bit;
    
    if (byte.length == 8) {
      var char = byte; // how can I convert this to a character again?
      byte = '';
      return char;
    }
    
    return '';
  }).join('');
}

alert(binaryToString('1110100110010111100111110100'));

How can I convert a byte into a character again? And it also feels a bit odd. Is there a better, faster way to collect those bytes

Answer 1

There is a problem with your stringToBinary function. Converting a character to binary only leaves you with the least amount of bits. So you still need to convert it to an 8-bit string.

The other thing is, that you can just get the first 8 digits from your binary and trim your input as you go, like in the following example.

function stringToBinary(input) {
  var characters = input.split('');

  return characters.map(function(char) {
    const binary = char.charCodeAt(0).toString(2)
    const pad = Math.max(8 - binary.length, 0);
    // Just to make sure it is 8 bits long.
    return '0'.repeat(pad) + binary;
  }).join('');
}

function binaryToString(input) {
  let bytesLeft = input;
  let result = '';

  // Check if we have some bytes left
  while (bytesLeft.length) {
    // Get the first digits
    const byte = bytesLeft.substr(0, 8);
    bytesLeft = bytesLeft.substr(8);

    result += String.fromCharCode(parseInt(byte, 2));
  }

  return result;
}

const binary = stringToBinary('test');
console.log({
  binary,
  text: binaryToString(binary),
});