base64url

This is a pure TypeScript Base64-URL encoder/decoder for JavaScript strings with UTF-8 support.

If you've found it, you're already aware that:

btoa and atob only work on ASCII strings, and they're not always available in cool new JS runtimes
Buffer is only in Node.js
TextEncoder only works in browsers

This implementation allows you to encode any JavaScript string (emojis and multi-byte characters allowed!) to and from UTF-8 and then encode it as Base64-URL. It's great for:

Working with JWTs on any JS runtime
Encoding JavaScript strings to UTF-8 when serializing or parsing binary formats

It's a no-dependencies / no-depends library. Just copy the src/base64url.ts file in your project. It's mostly finished software, so it's unlikely you'll need to update it.

Use

Base64-URL

To encode to Base64-URL:

import { stringToBase64URL } from "./base64url";

stringToBase64URL("This will be encoded to UTF-8 then Base64-URL");

To decode from Base64-URL:

import { stringFromBase64URL } from "./base64url";

stringFromBase64URL(
  "VGhpcyB3aWxsIGJlIGVuY29kZWQgdG8gVVRGLTggdGhlbiBCYXNlNjQtVVJM",
);

UTF-8

To encode a string to UTF-8:

import { stringToUTF8 } from "./base64url";

stringToUTF8("This will be encoded as UTF-8", (byte: number) => {
  // write this byte to a stream or buffer
});

To decode UTF-8 bytes to a string:

import { stringFromUTF8 } from "./base64url";

const result: string[] = [];
const state = { utf8seq: 0, codepoint: 0 };

const onCodepoint = (codepoint: number) => {
  result.push(String.fromCodePoint(codepoint));
};

for (let byte of buffer) {
  // buffer holds all the UTF-8 bytes,
  // call this function for each byte
  stringFromUTF8(byte, state, onCodepoint);
}

const string = result.join("");

supabase-community/base64url-js

base64url

Use

Base64-URL

UTF-8