Decode Base64 to Hexadecimal string with javascript

Question

Needing to convert a Base64 string to Hexadecimal with javascript.

Example:

var base64Value = \"oAAABTUAAg==\"

Need conversion m

Answer 1

Try

[...atob(base64Value)].map(c=> c.charCodeAt(0).toString(16).padStart(2,0))

let base64Value = "oAAABTUAAg=="

let h= [...atob(base64Value)].map(c=> c.charCodeAt(0).toString(16).padStart(2,0))

console.log( h.join``.toUpperCase() );

Answer 2

Assuming you want the hexadecimal representation as a string, the window.atob function (available in most modern browsers) is your first step - it will convert your base64 string to an ASCII string, where each character represents one byte.

At this point you split the string, grab the character code of each character, then convert that to a left-padded base-16 string.

function base64ToBase16(base64) {
  return window.atob(base64)
      .split('')
      .map(function (aChar) {
        return ('0' + aChar.charCodeAt(0).toString(16)).slice(-2);
      })
     .join('')
     .toUpperCase(); // Per your example output
}

console.log(base64ToBase16("oAAABTUAAg==")); // "A0000005350002"

(Or try it on JSBin)

Answer 3

Here is my vanilla JavaScript solution that does not use atob and Buffer. Supports separator, suitable for binary data and React Native, relatively high performance.

Usage :

base64ToHex( 'MTIzYWJjIDotKQ==', '-' )
// returns '31-32-33-61-62-63-20-3a-2d-29'

Code :

/* Convert base64 data to hex string.  https://stackoverflow.com/a/57909068/893578
 *   txt : Base64 string.
 *   sep : Hex separator, e.g. '-' for '1a-2b-3c'.  Default empty.
 */
const base64ToHex = ( () => {
   // Lookup tables
   const values = [], output = [];

   // Main converter
   return function base64ToHex ( txt, sep = '' ) {
      if ( output.length <= 0 ) populateLookups();
      const result = [];
      let v1, v2, v3, v4;
      for ( let i = 0, len = txt.length ; i < len ; i += 4 ) {
         // Map four chars to values.
         v1 = values[ txt.charCodeAt( i   ) ];
         v2 = values[ txt.charCodeAt( i+1 ) ];
         v3 = values[ txt.charCodeAt( i+2 ) ];
         v4 = values[ txt.charCodeAt( i+3 ) ];
         // Split and merge bits, then map and push to output.
         result.push(
            output[ ( v1 << 2) | (v2 >> 4) ],
            output[ ((v2 & 15) << 4) | (v3 >> 2) ],
            output[ ((v3 &  3) << 6) |  v4 ]
         );
      }
      // Trim result if the last values are '='.
      if ( v4 === 64 ) result.splice( v3 === 64 ? -2 : -1 );
      return result.join( sep );
   };

   function populateLookups () {
      const keys = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
      for ( let i = 0 ; i < 256 ; i++ ) {
         output.push( ( '0' + i.toString( 16 ) ).slice( -2 ) );
         values.push( 0 );
      }
      for ( let i = 0 ; i <  65 ; i++ )
         values[ keys.charCodeAt( i ) ] = i;
   }
} )();

Demo:

const [ txt, b64, hex, sep ] = document.querySelectorAll( 'input, select' );

function txtOnInput ({ target: { value }}) {
   hex.value = base64ToHex( b64.value = btoa( value ), sep.value ).toUpperCase();
}

function b64OnInput ({ target: { value }}) {
   hex.value = base64ToHex( value, sep.value ).toUpperCase();
   txt.value = atob( value );
}

txtOnInput({target:txt});

// Different coding style, same result.
function base64ToHex ( txt, sep = '' ) {
   let { val, out } = base64ToHex, v1, v2, v3, v4, result = [];
   if ( ! base64ToHex.val ) { // Populate lookup tables.
      out = base64ToHex.out = [];
      val = base64ToHex.val = Array( 255 ).fill( 0 );
      const keys = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
      for ( let i = 0 ; i < 256 ; i++ ) out.push( ( '0' + i.toString(16) ).slice( -2 ) );
      for ( let i = 0 ; i <  65 ; i++ ) val[ keys.charCodeAt( i ) ] = i;
   }
   for ( let i = 0, len = txt.length ; i < len ; i += 4 ) {
      v1 = val[ txt.charCodeAt( i   ) ]; // Map four chars to values.
      v2 = val[ txt.charCodeAt( i+1 ) ];
      v3 = val[ txt.charCodeAt( i+2 ) ];
      v4 = val[ txt.charCodeAt( i+3 ) ];
      result.push( out[ (v1 << 2) | (v2 >> 4) ], // Split values, map to output.
                   out[ ((v2 & 15) << 4) | (v3 >> 2) ],
                   out[ ((v3 & 3) << 6) | v4 ] );
   } // After loop ended: Trim result if the last values are '='.
   if ( v4 === 64 ) result.splice( v3 === 64 ? -2 : -1 );
   return result.join( sep ); // Array is fast.  String append = lots of copying.
}

label { display: block; height: 1em; }
input, select { position: absolute; left: 5em; width: calc( 100% - 6em ) }
input[readonly] { background: #D8D8D8; }

<label>Ascii <input oninput='txtOnInput(event)' value='123abc :-)'></label><br>
<label>Base64 <input oninput='b64OnInput(event)'></label><br>
<label>Hex    <input readonly></label><br>
<label> <select onchange='txtOnInput({target:txt})'>
<option value=''>(None)<option value=' ' selected>(Space)<option value='-'>-</select></label><br>

Note: this is done for geisterfurz007 because react-native-fs yields base64 for binary files, and (s)he needs to turn that into hex string. Not that I am happy with the efficiency of existing snippets...

Answer 4

atob() then charCodeAt() will give you binary & toString(16) will give you hex.

function base64ToHex(str) {
  const raw = atob(str);
  let result = '';
  for (let i = 0; i < raw.length; i++) {
    const hex = raw.charCodeAt(i).toString(16);
    result += (hex.length === 2 ? hex : '0' + hex);
  }
  return result.toUpperCase();
}

console.log(base64ToHex("oAAABTUAAg=="));

Answer 5

Why not try the following code?:

const buffer = Buffer.from(rawData, 'base64');
const bufString = buffer.toString('hex');