Issue #3268187 by Luke.Leber, darren.fisher: View of media items using OEmbed...

(function (Drupal, drupalSettings) {

  let io_initialized = false;

  let observe = false;

  Drupal.behaviors.oembedLazyloadIntersectionObserver = {

    attach: function attach(context) {

      if (io_initialized) {

        return;

      }

      io_initialized = true;

      if (observe === false) {

        // Check for IntersectionObserver support.

        // @see https://github.com/w3c/IntersectionObserver/blob/7382ce7e834c57ea166081484bd8f8a6de84de04/polyfill/intersection-observer.js#L16

        const modern_support =

          'IntersectionObserverEntry' in window &&

          'intersectionRatio' in window.IntersectionObserverEntry.prototype;

      const observe = (function () {

        observe = (function () {

          if (modern_support) {

            // Create an intersection observer that swaps out the src attribute.

            };

          }

        })();

      }

      // Set the observer to watch each eligible iframe.

      const videos = context.querySelectorAll('.oembed-lazyload[data-strategy="intersection-observer"]');