JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="clearInterval(interval)">Stop intreval</button>
Delay duration: <span id="delay_duration"></span>
<div id="output">

</div>

JavaScript

var j = 0;
  var interval = setInterval( function(){ 
      document.getElementById("output").innerHTML = ++j;
      
      if ( j === 10) {
    
      var date_before_delay = new Date();
    for (var i = 0; i < 1000000000*2; i++)
        ;
        var date_after_delay = new Date();

          document.getElementById("delay_duration").innerHTML = date_after_delay - date_before_delay;
          

    }
  }, 300);