JavaScript progress bar unhides but won't update

Question

I want a progress bar to unhide when the button is pressed and then to update. However, with the following code the progress bar shows but does not update.

If I remove style="display: none" the bar updates as expected. Any ideas?

document.getElementById("submit-btn").addEventListener("click", function() {
  document.getElementById("progress-top").style.display = 'block';

  var i = 0;
  if (i == 0) {
    i = 1;
    var width = 1;
    var id = setInterval(frame, 50);

    function frame() {
      if (width >= 100) {
        clearInterval(id);
        i = 0;
      } else {
        width++;
        document.getElementsByClassName('progress-bar').item(0).setAttribute('aria-valuenow', width);
        document.getElementsByClassName('progress-bar').item(0).setAttribute('style', 'width:' + Number(width) + '%');
      }
    }
  }


})

<div class="progress" style="display: none" id="progress-top">
  <div class="progress-bar" role="progressbar" aria-valuenow="" aria-valuemin="0" aria-valuemax="100">
  </div>
</div>

I'm using Bootstrap 4 for the CSS

.progress {
  display: flex;
  height: $progress-height;
  overflow: hidden; // force rounded corners by cropping it
  font-size: $progress-font-size;
  background-color: $progress-bg;
  @include border-radius($progress-border-radius);
  @include box-shadow($progress-box-shadow);
}

.progress-bar {
  display: flex;
  flex-direction: column;
  justify-content: center;
  color: $progress-bar-color;
  text-align: center;
  background-color: $progress-bar-bg;
  @include transition($progress-bar-transition);
}

Answer 1

Consider using the <progress> element were you just need to se the value.

To prevent starting the loop twice, consider checking the PID.

let id = null;

document.getElementById("submit-btn").addEventListener("click", function() {

    document.getElementById("progress-top").style.display = 'block';
       
    if (id === null) {
        var val = 1;
        id = setInterval(frame, 50);

        function frame() {
            if (val >= 100) {
                clearInterval(id);
                id = null;
            } else {
                val++;
                document.getElementById('progress').setAttribute('value', val);
            }
        }
    }
})

.progress {
    height: 150px;
}

<div class="progress" style="display: none" id="progress-top">
    <progress id="progress" value="0" max="100">0%</progress>
</div>

<button id='submit-btn'>Click me</button>

---

Regarding the Bootstap variant, you'll need to set both style.width and innerHTML.

The aria-valuenow doesn't need to be updated.

let id = null;

document.getElementById("submit-btn").addEventListener("click", function() {

    document.getElementById("progress-top").style.display = 'block';
       
    if (id === null) {
        var val = 1;
        id = setInterval(frame, 50);

        function frame() {
            if (val >= 100) {
                clearInterval(id);
                id = null;
            } else {
                val++;
                document.getElementsByClassName('progress-bar')[0].style.width = val + '%';
                document.getElementsByClassName('progress-bar')[0].innerHTML = val + '%';
            }
        }
    }
})

.progress {
    height: 150px;
    width: 200px;
}

<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/js/bootstrap.min.js"></script>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/css/bootstrap.min.css" rel="stylesheet"/>

<div class="progress" id="progress-top" style="display: none">
  <div class="progress-bar" role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100"></div>
</div>

<button id='submit-btn'>Click me</button>