JSFiddle - React, Tailwind, and code Playground

HTML

<button onclick="mouseup()">Run Code
</button>
<button onclick="pause()">Pause Code
</button>

JavaScript

let flag = 0;
const delay = 300;
const totalStps = 102;
var curStp = 0;

function mouseup() {
  let i = 0;
  console.log("Value of flag " + flag);
  while(i < totalStps - curStp) {
    const j = i;
    var timeout = setTimeout(function(){
       let stp = curStp;
       console.log("i " + i + "  j " + j + " curStp " + curStp);
       
       curStp = stp+1;   // this is done by setState.
       console.log("flag " + flag + " timeout " + timeout);
        }, delay * i);
        
    if (flag === 1) {
       console.log("break the loop");
       clearTimeout(timeout);
       // This is not stopping this setTimeout
       break;
    }
    i++;
  } 
}

function pause() {
  flag = 1;
  console.log("Value of flag in pause()  " + flag + " curStp " + curStp);
  let stp = curStp;
  curStp = stp;   // this is done by setState.
}