[javascript] ArrayBuffer to base64 encoded string

I need an efficient (read native) way to convert an ArrayBuffer to a base64 string which needs to be used on a multipart post.

The OP did not specify the Running Enviroment but if you are using Node.JS there is a very simple way to do such thing.

Accordig with the official Node.JS docs https://nodejs.org/api/buffer.html#buffer_buffers_and_character_encodings

// This step is only necessary if you don't already have a Buffer Object
const buffer = Buffer.from(yourArrayBuffer);

const base64String = buffer.toString('base64');

Also, If you are running under Angular for example, the Buffer Class will also be made available in a Browser Environment.

For those who like it short, here's an other one using Array.reduce which will not cause stack overflow:

var base64 = btoa(
  new Uint8Array(arrayBuffer)
    .reduce((data, byte) => data + String.fromCharCode(byte), '')
);

By my side, using Chrome navigator, I had to use DataView() to read an arrayBuffer

function _arrayBufferToBase64( tabU8A ) {
var binary = '';
let lecteur_de_donnees = new DataView(tabU8A);
var len = lecteur_de_donnees.byteLength;
var chaine = '';
var pos1;
for (var i = 0; i < len; i++) {
    binary += String.fromCharCode( lecteur_de_donnees.getUint8( i ) );
}
chaine = window.btoa( binary )
return chaine;}

There is another asynchronous way use Blob and FileReader.

I didn't test the performance. But it is a different way of thinking.

function arrayBufferToBase64( buffer, callback ) {
    var blob = new Blob([buffer],{type:'application/octet-binary'});
    var reader = new FileReader();
    reader.onload = function(evt){
        var dataurl = evt.target.result;
        callback(dataurl.substr(dataurl.indexOf(',')+1));
    };
    reader.readAsDataURL(blob);
}

//example:
var buf = new Uint8Array([11,22,33]);
arrayBufferToBase64(buf, console.log.bind(console)); //"CxYh"

function _arrayBufferToBase64( buffer ) {
    var binary = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++) {
        binary += String.fromCharCode( bytes[ i ] );
    }
    return window.btoa( binary );
}

but, non-native implementations are faster e.g. https://gist.github.com/958841 see http://jsperf.com/encoding-xhr-image-data/6

I used this and works for me.

function arrayBufferToBase64( buffer ) {
    var binary = '';
    var bytes = new Uint8Array( buffer );
    var len = bytes.byteLength;
    for (var i = 0; i < len; i++) {
        binary += String.fromCharCode( bytes[ i ] );
    }
    return window.btoa( binary );
}



function base64ToArrayBuffer(base64) {
    var binary_string =  window.atob(base64);
    var len = binary_string.length;
    var bytes = new Uint8Array( len );
    for (var i = 0; i < len; i++)        {
        bytes[i] = binary_string.charCodeAt(i);
    }
    return bytes.buffer;
}

You can derive a normal array from the ArrayBuffer by using Array.prototype.slice. Use a function like Array.prototype.map to convert bytes in to characters and join them together to forma string.

function arrayBufferToBase64(ab){

    var dView = new Uint8Array(ab);   //Get a byte view        

    var arr = Array.prototype.slice.call(dView); //Create a normal array        

    var arr1 = arr.map(function(item){        
      return String.fromCharCode(item);    //Convert
    });

    return window.btoa(arr1.join(''));   //Form a string

}

This method is faster since there are no string concatenations running in it.

This works fine for me:

var base64String = btoa(String.fromCharCode.apply(null, new Uint8Array(arrayBuffer)));

In ES6, the syntax is a little simpler:

let base64String = btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)));

As pointed out in the comments, this method may result in a runtime error in some browsers when the ArrayBuffer is large. The exact size limit is implementation dependent in any case.

Below are 2 simple functions for converting Uint8Array to Base64 String and back again

arrayToBase64String(a) {
    return btoa(String.fromCharCode(...a));
}

base64StringToArray(s) {
    let asciiString = atob(s);
    return new Uint8Array([...asciiString].map(char => char.charCodeAt(0)));
}

var blob = new Blob([arrayBuffer])

var reader = new FileReader();
reader.onload = function(event){
   var base64 =   event.target.result
};

reader.readAsDataURL(blob);

My recommendation for this is to NOT use native btoa strategies—as they don't correctly encode all ArrayBuffer's…

rewrite the DOMs atob() and btoa()

Since DOMStrings are 16-bit-encoded strings, in most browsers calling window.btoa on a Unicode string will cause a Character Out Of Range exception if a character exceeds the range of a 8-bit ASCII-encoded character.

While I have never encountered this exact error, I have found that many of the ArrayBuffer's I have tried to encode have encoded incorrectly.

I would either use MDN recommendation or gist.

• https://github.com/beatgammit/base64-js
• https://gist.github.com/jonleighton/958841

function _arrayBufferToBase64(uarr) {
    var strings = [], chunksize = 0xffff;
    var len = uarr.length;

    for (var i = 0; i * chunksize < len; i++){
        strings.push(String.fromCharCode.apply(null, uarr.subarray(i * chunksize, (i + 1) * chunksize)));
    }

    return strings.join("");
}

This is better, if you use JSZip for unpack archive from string