How to do Base64 Encoding in Javascript

In this article, you’ll learn how to encode a string to Base64 encoded format. Javascript has a built-in function named btoa() (binary-to-ascii) that you can use to perform Base64 encoding.

Base64 Encoding in Javascript (Works for UTF-8 strings: 8-bit bytes)

The following example shows how to Base64 encode a string using the built-in btoa() function -

var str = "hello:world!?$*&()'-=@~";

// Encode the String
var encodedString = btoa(str);
console.log(encodedString); // aGVsbG86d29ybGQhPyQqJigpJy09QH4=

The default btoa() function works well for binary data consisting of 8-bit bytes. However, if the input exceeds the 8-bit byte range (e.g. UTF-16), then it throws a Character Out Of Range exception.

Here is an example -

var str = "Hello 😊";

// Encode the String
var encodedString = btoa(str);
# Output
Uncaught DOMException: Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range

Generic Base64 Encoding with support for 16-bit encoded strings

To handle Unicode characters, you need to first escape the string somehow to an array of 8-bit bytes and then use window.btoa() function to encode to Base64.

Here is one approach:

function base64EncodeUnicode(str) {
    // First we escape the string using encodeURIComponent to get the UTF-8 encoding of the characters, 
    // then we convert the percent encodings into raw bytes, and finally feed it to btoa() function.
    utf8Bytes = encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function(match, p1) {
            return String.fromCharCode('0x' + p1);

    return btoa(utf8Bytes);

base64EncodeUnicode('Hello 😊')   // SGVsbG8g8J+Yig==

Using a Library to perform Base64 encoding safely

You can also use a library to perform Base64 encoding and decoding safely. These libraries support encoding and decoding of Unicode characters -

Also Read: Javascript Base64 Decode Example