Using Javascript's atob to decode base64 doesn't properly decode utf-8 strings

Javascript's atob can properly decode base64 strings that have been encoded with ASCII characters, for example, window.atob('YQ==') will return the ASCII character 'a'. However, it won't properly decode base64 strings that have been encoded with UTF-8 Unicode characters, for example, window.atob('4pyTIMOgIGxhIG1vZGU=') will return '⢠à la mode' instead of '✓ à la mode'.

To properly decode a base64 string that has been encoded with UTF-8, we need to use the escape and unescape functions. In this case, window.atob(unescape(encodeURIComponent('✓ à la mode'))) will return '4pyTIMOgIGxhIG1vZGU=' and window.atob('4pyTIMOgIGxhIG1vZGU=') will return '✓ à la mode'.

Another option to handle the incoming base64-encoded stream so that it's decoded as utf-8 is to use the TextDecoder class. This class provides a way to decode a base64-encoded string into a UTF-8 string. Here's an example of how to use it:

const text = '4pyTIMOgIGxhIG1vZGU=';
const decoder = new TextDecoder('utf-8');
const decodedText = decoder.decode(Uint8Array.from(atob(text)));
console.log(decodedText); // '✓ à la mode'