btoa('café') gives you the wrong bytes, and nothing tells you

Run this in your browser console: btoa('café'); // 'Y2Fm6Q==' Now encode the same word as UTF-8 first: btoa(String.fromCharCode(...new TextEncoder().encode('café'))); // 'Y2Fmw6k=' Same word, two different answers. Both are valid base64. Neither one throws. Only the second is what everyone else means by "café in base64". Why this happens btoa and...