JavaScript로 페이지를 로드하는 동안 진행률 표시줄을 어떻게 구현할 수 있나요?

<code class="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;
        // Update the progress bar with the calculated percentage
        console.log(percentComplete);
      }
    }, false);
    //Download progress
    xhr.addEventListener("progress", function(evt) {
      if (evt.lengthComputable) {
        var percentComplete = evt.loaded / evt.total;
        // Update the progress bar with the calculated percentage
        console.log(percentComplete);
      }
    }, false);
    return xhr;
  },
  type: 'POST',
  url: "/",
  data: {},
  success: function(data) {
    //Do something success-ish
  }
});</code>

<code class="javascript">$("#progress-bar").css("width", percentComplete * 100 + "%");</code>