JSFiddle - React, Tailwind, and code Playground

JavaScript

$.ajax({
  xhr: function()
  {
    var xhr = new window.XMLHttpRequest();
    //Upload progress
    xhr.upload.addEventListener("progress", function(evt){
      if (evt.lengthComputable) {
        var percentComplete = evt.loaded / evt.total;
        //Do something with upload progress
        console.log("up", percentComplete);
      }
    }, false);
    //Download progress
    xhr.addEventListener("progress", function(evt){
      if (evt.lengthComputable) {
        var percentComplete = evt.loaded / evt.total;
        //Do something with download progress
        console.log("down", percentComplete);
      }else{
        // the way jsFiddle's ajax echo service works the length
        // is not computable, so just adding this here:
        console.log("down", evt.loaded / 600000);
      }
    }, false);
    return xhr;
  },
  type: 'POST',
  url: "/echo/json/",
  data: {json: JSON.stringify(new Array(100000))},
  success: function(data){
      console.log(arguments);
    //Do something success-ish
  }
});