How can I convert an ArrayBuffer to a base64-encoded string?

Question

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

Answer 1

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

jsPerf.com is jsPerf.app now: https://jsperf.app/encoding-xhr-image-data/51

Updated benchmarks: https://jsben.ch/wnaZC

Answer 2

This works fine for me:

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

In ES6, the syntax is a little simpler:

const 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.

Answer 3

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), '')
);

Answer 4

The OP did not specify the Running Environment, but if you are using Node.JS there is a very simple way to do this.

According to 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.

Answer 5

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"

Answer 6

This example uses the built-in FileReader readDataURL() to do the conversion to base64 encoding. Data URLs are structured data:[<mediatype>][;base64],<data>, so we split that url at the comma and return only the base64 encoded characters.

const blob = new Blob([array]);        
const reader = new FileReader();

reader.onload = (event) => {
  const dataUrl = event.target.result;
  const [_, base64] = dataUrl.split(','); 
  // do something with base64
};
   
reader.readAsDataURL(blob);

Or as a promisified utility:

async function encode(array) {
  return new Promise((resolve) => {
    const blob = new Blob([array]);
    const reader = new FileReader();
    
    reader.onload = (event) => {
      const dataUrl = event.target.result;
      const [_, base64] = dataUrl.split(',');
      
      resolve(base64);
    };
    
    reader.readAsDataURL(blob);
  });
}

const encoded = await encode(typedArray);

Answer 7

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;
}

Answer 8

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

Answer 9

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)));
}

Answer 10

In Node.js (i.e. not browser):

Buffer.from(myArrayBuffer).toString("base64");

Answer 11

If you're okay with adding a library, base64-arraybuffer:

yarn add base64-arraybuffer

then:

• encode(buffer) - Encodes ArrayBuffer into base64 string
• decode(str) - Decodes base64 string to ArrayBuffer

Answer 12

Native method Uint8Array.prototype.toBase64 is now available!

Uint8Array.prototype.toBase64 has been implemented on most major browsers (see caniuse) and can be used as follows:

const arr = new Uint8Array([ 73, 32, 108, 111, 118, 101, 32, 121, 111, 117 ]);
const str = arr.toBase64();

console.log(str); // SSBsb3ZlIHlvdQ==

It's worth noting that since .toBase64 is a natively implemented function, it's incredibly fast (in fact, much faster than any of the top-voted answers).

---

You can also use this core-js polyfill:

const arr = new Uint8Array([ 73, 32, 108, 111, 118, 101, 32, 121, 111, 117 ]);
const base64 = arr.toBase64();

console.log(base64);

<script src="https://unpkg.com/[email protected]/minified.js"></script>

Answer 13

ABtoB64(ab) {
    return new Promise(res => {
        const fr = new FileReader();
        fr.onload = ({target: {result: s}}) => res(s.slice(s.indexOf(';base64,') + 8));
        fr.readAsDataURL(new Blob([ab]));
    });
}

asynchronous method using file reader.

Answer 14

i use TextDecode api to convert it to normal text and then convert it to Base64

const uint =  new Uint8Array([ 73, 32, 108, 111, 118, 101, 32, 121, 111, 117 ]).buffer
const decoder = new TextDecoder()
const decodedText = decoder.decode(uint)
const base64Code = btoa(decodedText)

Answer 15

In the Browser suggested solutions with btoa seem fine. But in Node.js btoa is Legacy

It is recommended to use buffer.toString(encoding)

like

const myString = buffer.toString("base64")

Answer 16

Here is a ES6 solution that is 3 times faster than using the native btoa function and is 1.25 faster than the non-native solution proposed by mobz and Emmanuel. Its code also respect more recent good coding practices and uses way more clean binary masks for readability :

    /**
     * @param {ArrayBuffer} buffer
     * @return {string}
     */
    function toBase64(buffer) {
        const base64Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

        const byteLength = buffer.byteLength;
        const bufferView = new Uint8Array(buffer);
        const remainingBytesCount = byteLength % 3;
        const mainLength = byteLength - remainingBytesCount;

        let string = "";
        let i = 0;

        for (; i < mainLength; i += 3) {
            const chunk = (bufferView[i] << 16) | (bufferView[i + 1] << 8) | bufferView[i + 2];
            string += base64Chars[(chunk & 0b111111000000000000000000) >> 18];
            string += base64Chars[(chunk & 0b000000111111000000000000) >> 12];
            string += base64Chars[(chunk & 0b000000000000111111000000) >> 6];
            string += base64Chars[(chunk & 0b000000000000000000111111)];
        }

        if (remainingBytesCount === 2) {
            const chunk = (bufferView[i] << 16) | (bufferView[i + 1] << 8);
            string += base64Chars[(chunk & 0b111111000000000000000000) >> 18];
            string += base64Chars[(chunk & 0b000000111111000000000000) >> 12];
            string += base64Chars[(chunk & 0b000000000000111111000000) >> 6];
            string += "=";

        } else if (remainingBytesCount === 1) {
            const chunk = (bufferView[i] << 16);
            string += base64Chars[(chunk & 0b111111000000000000000000) >> 18];
            string += base64Chars[(chunk & 0b000000111111000000000000) >> 12];
            string += "==";
        }

        return string;
    }

Answer 17

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.

Answer 18

 var uint8Array = new Uint8Array(BytesArray);

 var base64Str = btoa(String.fromCharCode(...uint8Array));

 Or,

 var base64Str = btoa(uint8Array.reduce((x, y) => x + String.fromCharCode(y), ''));

Answer 19

Use uint8-to-b64 package to do encoding/decoding in browser and Node.js

Answer 20

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;}

Answer 21

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