[Javascript] Ajax 통신 progress bar

 xhr: function () {
        var xhr = new window.XMLHttpRequest();
        xhr.upload.addEventListener(
          "progress",
          function (evt) {
            if (evt.lengthComputable) {
              var percentComplete = evt.loaded / evt.total;
              setProgress(percentComplete);
            }
          },
          false
        );
        xhr.addEventListener(
          "progress",
          function (evt) {
            if (evt.lengthComputable) {
              var percentComplete = evt.loaded / evt.total;
              setProgress(percentComplete);
            }
          },
          false
        );

        return xhr;
      },

참고 : https://codepen.io/alexpetergill/pen/XdGjGd

jQuery: AJAX progress bar