demo/index.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Sticky-Observer Playground</title>
    <script src="../dist/sticky-observer.js"></script>

    <style>
      body {
        margin: 0;
        padding: 0;
        border: 0;
        font-family: sans-serif;
        font-size: 5rem;
      }

      .sticky-element {
        color: red;
      }

      .sticky-element--is-sticky {
        position: fixed;
        top: 0;
        color: white;
      }

      .sticky-element__placeholder {
        height: 500px !important;
        background: red;
      }
    </style>
  </head>

  <body>
    <header style="height: 100px; background: lightblue">Header</header>
    <div class="container" style="height: 500px;">
      <div
        class="sticky-element"
        data-sticky-class="sticky-element--is-sticky"
        data-sticky-placeholder-class="sticky-element__placeholder"
      >
        Element
      </div>
    </div>
    <footer style="height: 1000px;background: lightblue">Footer</footer>

    <script>
      var stickyContainer = document.querySelector('.container');
      var stickyElement = document.querySelector('.sticky-element');
      var stickyObserver = new sticky.StickyObserver([stickyElement], stickyContainer);

      stickyObserver.init();

      stickyObserver.onStateChange(function(event) {
        switch (event.nextState) {
          case sticky.StickyState.STICKY:
            event.element.sticky.addPlaceholder();
            event.element.sticky.addStickyClass();
            break;
          case sticky.StickyState.NORMAL:
            event.element.sticky.removePlaceholder();
            event.element.sticky.removeStickyClass();
            break;
          case sticky.StickyState.STICKY_END_OF_CONTAINER:
            event.element.sticky.removePlaceholder();
            event.element.sticky.removeStickyClass();
            break;
          default:
            // ignore
            break;
        }
      });

      stickyObserver.observe();
    </script>
  </body>
</html>