How to Base64 encode and decode in Node.js#

Here is how you encodetext to base64 in Node.js:

var b = new Buffer('JavaScript');
var s = b.toString('base64');
// SmF2YVNjcmlwdA==

And here is how you decode base64 encoded strings:

var b = new Buffer('SmF2YVNjcmlwdA==', 'base64')
var s = b.toString();
// JavaScript

If you are interested in the details of how the above examples worked, follow me.

The Buffer() constructor requires a number, array or string as the first parameter, and an optional encoding type as the second parameter. The possible encoding types are ascii, utf8, ucs2, base64, binary, and hex, the default being utf8.

By passing the second parameter, we tell JavaScript that "the string you see is encoded in this particular format". Notice how we did that in the decoding example.

Once we have the encoded string, we call the toString() method on the string. If we don't pass the encoding type to toString(), Node.js assumes we want to convert the object to utf8 encoded string by default. We can make it convert to other formats by passing the encoding type to toString().

Let's encode a base64 encoded string to hex:

var b = new Buffer('SmF2YVNjcmlwdA==', 'base64')
var s = b.toString('hex');
// 4a617661536372697074

Now decode it to something humans can read:

var b = new Buffer('4a617661536372697074', 'hex')
var s = b.toString('utf8');
// JavaScript

Once you get the basics of Buffer and encoding, you can use your knowledge of the File System module to encode files to base64 strings.

In this well-commented example we convert an image to base64 encoded string, and re-generate a copy of the image from the base64 encoded string.

var fs = require('fs');

// function to encode file data to base64 encoded string
function base64_encode(file) {
 // read binary data
 var bitmap = fs.readFileSync(file);
 // convert binary data to base64 encoded string
 return new Buffer(bitmap).toString('base64');

// function to create file from base64 encoded string
function base64_decode(base64str, file) {
  // create buffer object from base64 encoded string, it is important to tell the constructor that the string is base64 encoded
 var bitmap = new Buffer(base64str, 'base64');
 // write buffer to file
 fs.writeFileSync(file, bitmap);
 console.log('******** File created from base64 encoded string ********');

// convert image to base64 encoded string
var base64str = base64_encode('kitten.jpg');
// convert base64 string back to image
base64_decode(base64str, 'copy.jpg');


I am sure you learnt not only how to encode and decode base64, but in many other formats as well. Have fun with encoding!

UTF-8 is the superset of ASCII. If you are limited to using characters on the standard English keyboard, you can use ascii; if you are dealing with 'exotic' characters and symbols like ⌘, こんにちは, Üdvözöljük etc., use UTF-8.


  1. Wikipedia - Base64
  2. Wikipedia - ASCII
  3. Wikipedia - UTF-8
  4. Node.js - Buffer
Tweet this | Share on LinkedIn |