# How might window.btoa() be implemented in JS?

```javascript
/**
 * @param {string} b
 * @returns {string}
 */
const btoa = (b) => {
	let s = '';

	const bytes = new Uint8Array(b.split('').map(x => x.charCodeAt(0)));
	const ALPHABET_TABLE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

	for (let i = 0; i < bytes.length; i += 3) {
		const group = new Uint8Array(
			[
				bytes.at(i) ?? 0x00,
				bytes.at(i+1) ?? 0x00,
				bytes.at(i+2) ?? 0x00,
			],
		);

		const egroup = new Uint8Array(4);

		egroup[0] = (group[0] >> 2) & 0x3f;
		egroup[1] = (((group[0] << 6) | (group[1] >> 2)) >> 2) & 0x3f;
		egroup[2] = (((group[1] << 4) | (group[2] >> 4)) >> 2) & 0x3f;
		egroup[3] = group[2] & 0x3f;

		if (bytes.at(i+2) == undefined) egroup[3] = 64;
		if (bytes.at(i+1) == undefined) egroup[2] = egroup[3] = 64;

		s += ALPHABET_TABLE[egroup[0]];
		s += ALPHABET_TABLE[egroup[1]];
		s += ALPHABET_TABLE[egroup[2]];
		s += ALPHABET_TABLE[egroup[3]];
	}

	return s;
};

console.log(
	btoa('The quick brown fox jumps over the brown dog'),
);
```

[https://gist.github.com/fuadop/63a7fc0e032176103e70e45c21b79375](https://gist.github.com/fuadop/63a7fc0e032176103e70e45c21b79375)