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Encode an ArrayBuffer as a base64 string
// Converts an ArrayBuffer directly to base64, without any intermediate 'convert to string then
// use window.btoa' step. According to my tests, this appears to be a faster approach:
// http://jsperf.com/encoding-xhr-image-data/5
/*
MIT LICENSE
Copyright 2011 Jon Leighton
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
function base64ArrayBuffer(arrayBuffer) {
var base64 = ''
var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
var bytes = new Uint8Array(arrayBuffer)
var byteLength = bytes.byteLength
var byteRemainder = byteLength % 3
var mainLength = byteLength - byteRemainder
var a, b, c, d
var chunk
// Main loop deals with bytes in chunks of 3
for (var i = 0; i < mainLength; i = i + 3) {
// Combine the three bytes into a single integer
chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2]
// Use bitmasks to extract 6-bit segments from the triplet
a = (chunk & 16515072) >> 18 // 16515072 = (2^6 - 1) << 18
b = (chunk & 258048) >> 12 // 258048 = (2^6 - 1) << 12
c = (chunk & 4032) >> 6 // 4032 = (2^6 - 1) << 6
d = chunk & 63 // 63 = 2^6 - 1
// Convert the raw binary segments to the appropriate ASCII encoding
base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d]
}
// Deal with the remaining bytes and padding
if (byteRemainder == 1) {
chunk = bytes[mainLength]
a = (chunk & 252) >> 2 // 252 = (2^6 - 1) << 2
// Set the 4 least significant bits to zero
b = (chunk & 3) << 4 // 3 = 2^2 - 1
base64 += encodings[a] + encodings[b] + '=='
} else if (byteRemainder == 2) {
chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1]
a = (chunk & 64512) >> 10 // 64512 = (2^6 - 1) << 10
b = (chunk & 1008) >> 4 // 1008 = (2^6 - 1) << 4
// Set the 2 least significant bits to zero
c = (chunk & 15) << 2 // 15 = 2^4 - 1
base64 += encodings[a] + encodings[b] + encodings[c] + '='
}
return base64
}
@Teamop
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Teamop commented Dec 7, 2018

based on https://developers.google.com/web/updates/2012/06/How-to-convert-ArrayBuffer-to-and-from-String,
a more easier way:

function bufferToBase64(buffer) {
     const binary = String.fromCharCode.apply(null, buffer);
     return window.btoa(binary);
}

@paschalidi
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paschalidi commented Feb 17, 2019

@Teamop this way wont work for ArrayBuffer larger than 30k bytes.

@paschalidi
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paschalidi commented Feb 17, 2019

I ended up using this

(function(){
  "use strict";

  var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  // Use a lookup table to find the index.
  var lookup = new Uint8Array(256);
  for (var i = 0; i < chars.length; i++) {
    lookup[chars.charCodeAt(i)] = i;
  }

  exports.encode = function(arraybuffer) {
    var bytes = new Uint8Array(arraybuffer),
    i, len = bytes.length, base64 = "";

    for (i = 0; i < len; i+=3) {
      base64 += chars[bytes[i] >> 2];
      base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
      base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
      base64 += chars[bytes[i + 2] & 63];
    }

    if ((len % 3) === 2) {
      base64 = base64.substring(0, base64.length - 1) + "=";
    } else if (len % 3 === 1) {
      base64 = base64.substring(0, base64.length - 2) + "==";
    }

    return base64;
  };

  exports.decode =  function(base64) {
    var bufferLength = base64.length * 0.75,
    len = base64.length, i, p = 0,
    encoded1, encoded2, encoded3, encoded4;

    if (base64[base64.length - 1] === "=") {
      bufferLength--;
      if (base64[base64.length - 2] === "=") {
        bufferLength--;
      }
    }

    var arraybuffer = new ArrayBuffer(bufferLength),
    bytes = new Uint8Array(arraybuffer);

    for (i = 0; i < len; i+=4) {
      encoded1 = lookup[base64.charCodeAt(i)];
      encoded2 = lookup[base64.charCodeAt(i+1)];
      encoded3 = lookup[base64.charCodeAt(i+2)];
      encoded4 = lookup[base64.charCodeAt(i+3)];

      bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
      bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
      bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
    }

    return arraybuffer;
  };
})();

@tinkotvas
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tinkotvas commented May 13, 2019

function bufferToBase64(buffer) {
     const binary = String.fromCharCode.apply(null, buffer);
     return window.btoa(binary);
}

@Teamop this way wont work for ArrayBuffer larger than 30k bytes.

While this thread was about "Converts an ArrayBuffer directly to base64, without any intermediate 'convert to string then use window.btoa' step" so I'm going a bit off topic, but there is a way to avoid the "larger than 30k bytes" issues using reduce.

bufferToBase64(buffer) {
    return btoa(new Uint8Array(buffer).reduce((data, byte)=> {
      return data + String.fromCharCode(byte);
    }, ''));
  }

Further example using this with angular7 for image source (say you're storing images in a database)

  bufferToBase64ImageSource(buffer) {
    const base64String = btoa(new Uint8Array(buffer).reduce((data, byte)=> {
      return data + String.fromCharCode(byte);
    }, ''));
    return this.domSanitzer.bypassSecurityTrustUrl('data:image/jpg;base64, ' + base64String);
  }

@bolmaster2
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bolmaster2 commented Apr 5, 2020

@Teamop this way wont work for ArrayBuffer larger than 30k bytes.

Can you elaborate why it wouldn't work? I've been using it successfully in both Firefox and Chrome?

@spalt08
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spalt08 commented Apr 30, 2020

I've made a benchmark: https://jsbench.me/vjk9nczxst/1

The code below shows stable and fast result among browsers.

function bufferToBase64(buffer) {
     const binary = String.fromCharCode.apply(null, buffer);
     return window.btoa(binary);
}

However, original approach is a little bit faster in Safari

@odbol
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odbol commented Aug 28, 2020

Warning: Using @spalt08's method with the recursion will fail with a RangeError: Maximum call stack size exceeded error for large buffers.

Better to use a good ol' for loop, like @hookenz. Sometimes functional programming is terribly inefficient.

@spalt08
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spalt08 commented Aug 31, 2020

@odbol
there is no recursion here. If your payload is big, String.fromCharCode.apply will overflow execution stack. You can use for loop for converting buffer to binary string in these cases

@hookenz
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hookenz commented Oct 22, 2020

@TFrascaroli - thanks for the feedback in 2016! As I recall I needed the utmost performance when converting a UTF-8 encoded string. It was something to do with encoding images for something like an MJPEG stream so performance was important and 40ms made a difference. Anyway, thanks for pointing out the differences.

@TFrascaroli
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TFrascaroli commented Nov 18, 2020

@hookenz To be perfectly frank, I don't even remember what I used this for. But I remember that I needed a way to convert binary data into base64, not just binary representation of a string, but actual binary data with a bunch of '\0's in it. Anyway, if I helped in any way I'm glad I could do so 👍

@wis
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wis commented Nov 20, 2020

I found that converting to a string (with String.fromCharCode) and then base64 encoding (with btoa) is faster, it may have changed
https://www.measurethat.net/Benchmarks/Show/10469/0/stringfromcharcode-btoa-vs-base64arraybuffer-function

edit: I just noticed and fixed a flaw in the test above, a new arraybuffer is being created in the function, and the whole point of this gist is avoiding copying. I fixed it here https://www.measurethat.net/Benchmarks/Show/10470/0/stringfromcharcode-btoa-vs-base64arraybuffer-function-f
turns out that base64 encoding an arraybuffer to string is faster than creating a DOMString then base64 encoding to a DOMstring.

edit2: with a big arraybuffer the performance tanks and performance of native String.fromCharCode stays more consistent
https://www.measurethat.net/Benchmarks/Show/10471/0/stringfromcharcode-btoa-vs-base64arraybuffer-function-f

@peterbajwa
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peterbajwa commented Nov 22, 2020

Can anyone please help me know, is this base64 conversion specific to Javascript or is equivalent to other languages Base64 conversion methods. eg. Ruby has below code to convert the byte array to base64 string.
array.pack('C*').force_encoding('UTF-8')

@TFrascaroli
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TFrascaroli commented Nov 22, 2020

@peterbajwa Base64 is base64, no matter who produces it or who consumes it. That's the beauty of standards 😉

@TFrascaroli
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TFrascaroli commented Nov 22, 2020

@peterbajwa Base64 is base64, no matter who produces it or who consumes it. That's the beauty of standards 😉

@YATACOBLAS
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YATACOBLAS commented Apr 15, 2021

thank you !!! @jonleighton

@Github743
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Github743 commented Oct 3, 2021

When I am uploading a 10 MB file some how it is not giving any conversion. Here is what I am working on
https://jsfiddle.net/DorababuMeka/7g9yLrs3/29/

@yongky-utama
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yongky-utama commented Nov 10, 2021

@hookenz
I know it's been a long time, but as I tried to figure out why it didn't work, I found that in your loop, buffer[i] is always undefined.
It turned out that you just need to convert it to Uint8Array first.

function uint8ToBase64( 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 );
}

Which is the same as the top answer in this stack overflow topic: ( https://stackoverflow.com/questions/9267899/arraybuffer-to-base64-encoded-string )

It's correct as far as I can tell, as modern browsers allows '\x00' characters in JS Strings.

@EmanH
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EmanH commented Feb 25, 2022

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

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