JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" onclick="cleanupDOM('editable')" value="Cleanup">
<div id="editable" contenteditable="true">
<b><i>Hel</i><i>l</i></b><i><b>o World!</b></i><i>Hel</i><i>lo</i>
</div>

JavaScript

function getTextNodesIn(node) {
    var textNodes = [];
    if (node.nodeType == 3) {
        textNodes.push(node);
    } else {
        var children = node.childNodes;
        for (var i = 0, len = children.length; i < len; ++i) {
            textNodes.push.apply(textNodes, getTextNodesIn(children[i]));
        }
    }
    return textNodes;
}

function setSelectionRange(el, start, end) {
    if (document.createRange && window.getSelection) {
        var range = document.createRange();
        range.selectNodeContents(el);
        var textNodes = getTextNodesIn(el);
        var foundStart = false;
        var charCount = 0, endCharCount;

        for (var i = 0, textNode; textNode = textNodes[i++]; ) {
            endCharCount = charCount + textNode.length;
            if (!foundStart && start >= charCount && (start < endCharCount || (start == endCharCount && i < textNodes.length))) {
                range.setStart(textNode, start - charCount);
                foundStart = true;
            }
            if (foundStart && end <= endCharCount) {
                range.setEnd(textNode, end - charCount);
                break;
            }
            charCount = endCharCount;
        }

        var sel = window.getSelection();
        sel.removeAllRanges();
        sel.addRange(range);
    } else if (document.selection && document.body.createTextRange) {
        var textRange = document.body.createTextRange();
        textRange.moveToElementText(el);
        textRange.collapse(true);
        textRange.moveEnd("character", end);
        textRange.moveStart("character", start);
        textRange.select();
    }
}


function cleanupDOM(id) {
    var el = document.getElementById(id);
    var start = 1;
    var end = start+1;
    var len = el.textContent.length;
    console.log(len);
    while(end<len) {
        setSelectionRange(document.getElementById(id), start, end);
        var isBold = document.queryCommandState("Bold");
        var isItalic =...