JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="toolbar">
	<li><a href="javascript:void(null);" class="editor_button btn_bold">Fett</a></li>
	<li><a href="javascript:void(null);" class="editor_button btn_italic">Kursiv</a></li>
	<li><a href="javascript:void(null);" class="editor_button btn_deleted">Durchgestrichen</a></li>
</ul>
<div id="anzeige" contenteditable="true">
    Lorem ipsum <b>dol</b>or sit amet, consetetur <b>sadipscing elitr, <i>sed diam nonumy eirmod tempor invidunt ut labore</i> et dolore magna</b> aliquyam erat, sed diam voluptua. 
	At vero eos et accusam et justo duo dolores et ea rebum. <b>Stet clita kasd gubergren</b>, no sea takimata sanctus est Lorem ipsum dolor sit amet. 
	Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. 
	At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
</div>
<textarea id="html"></textarea>

JavaScript

$('#anzeige').keydown(function(e) {
    $("#html").val($("#anzeige").html().trim());
});

$(".btn_bold").click(function() { wrap('b'); });
$(".btn_italic").click(function() { wrap('i'); });
$(".btn_deleted").click(function() { wrap('s'); });

	function wrap(tag) {
	    var sel, range, laenge;
	    var tag_start = '<' + tag + '>';
	    var tag_ende = '</' + tag + '>';
	    var tag_temp = 'mark';     
		var html = "";

		if (typeof window.getSelection != "undefined") {
		    var range = window.getSelection().getRangeAt(0).cloneRange();
		    var container = document.createElement(tag_temp);
		    range.surroundContents(container);
			html = container.innerHTML;
			$(tag_temp).replaceWith(tag_start + html + tag_ende);
		} else if (typeof document.selection != "undefined") {
		    if (document.selection.type == "Text") {
		        html = document.selection.createRange().htmlText;
		    }
		}
	}