Streaming Data Updates with Flask

Integrating live data streams into HTML templates can pose challenges due to the static nature of templates rendered on the server. However, there are approaches to achieve this functionality.

To stream data without modifying the template dynamically, JavaScript can be employed. By issuing a request to a streaming endpoint, the client-side JavaScript can read and display the data in real time. This approach introduces complexity but offers greater control over the output appearance.

For example, the following code demonstrates how to display both the latest value and a log of all received values:

setInterval(() => {
  var latest = document.getElementById('latest');
  var output = document.getElementById('output');
  var xhr = new XMLHttpRequest();
  xhr.open('GET', '{{ url_for('stream') }}');
  xhr.send();
  var position = 0;

  function handleNewData() {
    var messages = xhr.responseText.split('\n');
    messages.slice(position, -1).forEach(function(value) {
      latest.textContent = value;
      var item = document.createElement('li');
      item.textContent = value;
      output.appendChild(item);
    });
    position = messages.length - 1;
  }

  timer = setInterval(function() {
    handleNewData();
    if (xhr.readyState === XMLHttpRequest.DONE) {
      clearInterval(timer);
      latest.textContent = 'Done';
    }
  }, 1000);
}, 1000);

Alternatively, an