TL;DR;
Your string is actually UTF-16, not UTF-8. Here's how to decode it properly.
function atob(b64txt) {
const buff = Buffer.from(b64txt, 'base64');
const txt = buff.toString('utf16le');
return txt;
}
Explanation: Your base64 encoded string isn't actually UTF-8 or ASCII data. It's UTF-16 (little-endian). That means every character always has two bytes.
UTF-8 is different: any byte that is less than 127 indicates a single-byte character. A byte greater than 127 would have a second byte, and if the second byte is > 127 there would be a third byte, etc.
So let's decode your string to character codes and see what it looks like:
const b64txt = 'VABpAG0AZQAgAHMAZQByAGUAaQBzAA==';
const buff = Buffer.from(b64txt, 'base64');
console.log(JSON.stringify(buff));
// >> {"type":"Buffer","data":[84,0,105,0,109,0,101,0,32,0,115,0,101,0,114,0,101,0,105,0,115,0]}
First character (84) is the ASCII character for T. But it's less than 127, and it still has a 0 byte following it. So...not UTF-8.
That's the clue that this string has two bytes per character, making it UTF-16. And the fact that the 0 follows the character is the clue that it's "little-endian" (the 0-255 byte comes first, and the 256-65536 byte comes second).
If you want to change this buffer into text, you need to interpret it as the correct type of string:
const txt = buff.toString('utf16le'); // <- UTF-16, little-endian
console.log(txt);
// >> "Time sereis"
So in node.js, if you combine those two commands, you end up with a full fledged solution to get your string decoded properly, as above in the TL;DR;.
Of course if your encoding type changes, you'd have to change this as well, and do toString('utf8') or whatever the appropriate encoding is.
(credit: I referenced this and this as I was drafting this answer.)
