JSFiddle - React, Tailwind, and code Playground

HTML

<div id='status'></div>

JavaScript

function print(string) {
  var statusElement = document.getElementById('status');
  statusElement.innerHTML += ('' + string);
}

var PIECE = 100;
function subProcess(start, end) {
  var i = 0, j = 0, finished = false;
  var f = [];
  // End comments meet.
  if (start >= end) {
    print('Finished');
    return;
  }

  var sub = function() {
    var count = 0;
    finished = true;
    for (; i < 100000; ++i) {
      for (; j < 100000; ++j) {
        f.push(1);
        ++count;
        if (count >= PIECE) {
          finished = false;
          break;
        }
      }
    }
    if (finished) {
        // Print status.
      print(start);
        // Start Next part.
      subProcess(start + 1, end);
      return;
    }
    setTimeout(sub, 10);
  }
  setTimeout(sub, 10);
}
subProcess(1, 8);