Which Characters Are Supported by the JavaScript btoa() Method?

The JavaScript btoa() method only supports characters that can be represented using a single byte (8-bits). This means that it only supports a total of 256 characters from the following character sets:

1. 128 characters of the ASCII character set, and;
2. 128 characters of the Latin-1 (ISO-8859-1) character set.

For example:

// ES5+
const encodedStr = btoa('foobar');
console.log(encodedStr); // 'Zm9vYmFy'

If you pass a string that is not in this range to the btoa() method, it will throw an error:

// ES5+
// Uncaught DOMException: Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.
btoa('🦊');

To support multibyte strings, you can convert the original string to binary format so that it can be used with the btoa() method for Base64 encoding.