notifications-admin/app/assets/javascripts/updateContent.js

(function(Modules) {
  "use strict";

  var queues = {};
  var dd = new diffDOM.DiffDOM();

  var getRenderer = $component => response => dd.apply(
    $component.get(0),
    dd.diff($component.get(0), $(response[$component.data('key')]).get(0))
  );

  var getQueue = resource => (
    queues[resource] = queues[resource] || []
  );

  var flushQueue = function(queue, response) {
    while(queue.length) queue.shift()(response);
  };

  var clearQueue = queue => (queue.length = 0);

  var poll = function(renderer, resource, queue, interval, form) {

    if (document.visibilityState !== "hidden" && queue.push(renderer) === 1) $.ajax(
      resource,
      {
        'method': form ? 'post' : 'get',
        'data': form ? $('#' + form).serialize() : {}
      }
    ).done(
      response => flushQueue(queue, response)
    ).fail(
      () => poll = function(){}
    );

    setTimeout(
      () => poll(...arguments), interval
    );
  };

  Modules.UpdateContent = function() {

    this.start = component => poll(
      getRenderer($(component)),
      $(component).data('resource'),
      getQueue($(component).data('resource')),
      ($(component).data('interval-seconds') || 1.5) * 1000,
      $(component).data('form')
    );

  };

})(window.GOVUK.Modules);