JSFiddle - React, Tailwind, and code Playground

HTML

<script>
	function utf8_to_b64( str ) {
		return window.btoa(encodeURIComponent( escape( str )));
	}

	function b64_to_utf8( str ) {
		return unescape(decodeURIComponent(window.atob( str )));
	}
	
	function convert() {
		var str = document.getElementById("text").value;
		document.getElementById("converted_text").value = utf8_to_b64(str);
	}
</script>
<label for="text" style="display:block;">enter some text:</label>
<textarea id="text"></textarea><p/>

<label for="converted_text" style="display:block;">base64:</label>
<textarea id="converted_text"></textarea>

<input type="button" value="Convert" onClick="convert();"/>