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

Possible duplicate of [Converting Binary to text using javascript](https://stackoverflow.com/questions/21354235/converting-binary-to-text-using-javascript) — Tigger, Nov 11 '18 at 10:04

lumio · Accepted Answer · 2022-05-10T09:50:31.047

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),
});

Thanks, that really helped! I didn't know that I need leading zeros here. — ger616c64, Nov 11 '18 at 10:38
When you use a transpiler (like babel) or you don't care about IE11 you can also use `padStart` like in Nina Scholz' answer. — lumio, Nov 11 '18 at 10:53

Nina Scholz · Answer 2 · 2018-11-11T10:50:38.107

First of all, you need to take the same length of the converted string as input for the conversion back to a string, by taking String#padStart with a length of 8 and a filling character of zero.

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

    return characters
        .map(function(char) {
            return char.charCodeAt(0).toString(2).padStart(8, 0)
        })
        .join(' '); // show with space for each byte
                    // watch leading zero, which is missed in the former code
}

console.log(stringToBinary('test'))

The you need to take this string and split it into a length of eight characters and convert it back.

function binaryToString(input) {
    return input
        .match(/.{8}/g)                                    // take 8 characters
        .map(function(byte) {
            return String.fromCharCode(parseInt(byte, 2));
        })
        .join('');
}

console.log(binaryToString('01110100011001010111001101110100'));

While you are asking for a faster way, you could spread the splitted converted bytes to the fromCharCode function.

function binaryToString(input) {
    return String
        .fromCharCode(...input
            .match(/.{8}/g)
            .map(byte => parseInt(byte, 2))
        );
}

console.log(binaryToString('01110100011001010111001101110100'));

Thank you! That really helps. I didn't know that I need leading zeros. So is your solution expecting me to create the binary string with spaces? — ger616c64, Nov 11 '18 at 10:37
no, it is just to show the leading zero and the length of eight characters. — Nina Scholz, Nov 11 '18 at 10:49

score 0 · Answer 3 · edited Feb 03 '21 at 01:49

I just worked on exact project right now, here are the functions to convert from text to binary and from binary to text:

function binaryToTexttConverter(str) {
  let wordArray = [];
  let message = str.split(" ").map((stack) => {
    let numberArray = parseInt(stack, 2);
    let letters = String.fromCharCode(numberArray);
    wordArray.push(letters);
  });
  let output = wordArray.join("");
  console.log(output);
  return output;
}

// binaryToTexttConverter("test binary"); 

*****************************************************************

function textToBinaryConverter(str) {
  let xterCodesArray = [];
  let splitted = str.split("");
  for (i = 0; i < splitted.length; i++) {
    let xterCodes = splitted[i].charCodeAt(splitted[i]);
    xterCodesArray.push(xterCodes.toString(2));
  }
  console.log(xterCodesArray.join(" "));
  return xterCodesArray.join(" ");
}

// textToBinaryConverter("test string");

Converting a string into binary and back

3 Answers3