JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  blah blah
  <span>285blahblah</span>
</div>
<h1></h1>

JavaScript

var html= document.getElementsByTagName('div')[0].innerHTML;// or $('div').html() if jquery
var number = parseFloat(html.match(/-*[0-9]+/));
window.onload = function(){ 
    document.getElementsByTagName('h1')[0].innerHTML="extracted: "+number;
}