JSFiddle - React, Tailwind, and code Playground

HTML

<mark class=obj><u><a>т</a><strike><b>уп</b><a>и</a></strike><a>к</a></u></mark>

<div id=w></div>

JavaScript

var obj = document.getElementsByClassName('obj')[0];

Recurs(obj);

function Recurs(obj) {
	if ( obj.nodeType === 3) w.innerText = w.innerText + obj.textContent;	
	else for (var i = 0; i < obj.childNodes.length; i++) Recurs(obj.childNodes[i]);
}