jsdomabab 
A JavaScript module that implements window.atob and window.btoa according the forgiving-base64 algorithm in the Infra Standard. The original code was forked from w3c/web-platform-tests.
Compatibility: Node.js version 3+ and all major browsers.
Install with npm:
npm install abab
API
btoa (base64 encode)
const { btoa } = require('abab');
btoa('Hello, world!'); // 'SGVsbG8sIHdvcmxkIQ=='
atob (base64 decode)
const { atob } = require('abab');
atob('SGVsbG8sIHdvcmxkIQ=='); // 'Hello, world!'
Valid characters
Per the spec, btoa will accept strings "containing only characters in the range U+0000 to U+00FF." If passed a string with characters above U+00FF, btoa will return null. If atob is passed a string that is not base64-valid, it will also return null. In both cases when null is returned, the spec calls for throwing a DOMException of type InvalidCharacterError.
Browsers
If you want to include just one of the methods to save bytes in your client-side code, you can require the desired module directly.
const atob = require('abab/lib/atob');
const btoa = require('abab/lib/btoa');
Development
If you're submitting a PR or deploying to npm, please use the checklists in CONTRIBUTING.md.
Remembering what atob and btoa stand for
Base64 comes from IETF RFC 4648 (2006).
btoa, the encoder function, stands for binary to ASCII, meaning it converts any binary input into a subset of ASCII (Base64).atob, the decoder function, converts ASCII (or Base64) to its original binary format.