sousa-gecko/testing/web-platform/tests/css/cssom-view/scroll-behavior-smooth-navigation.html

<!DOCTYPE html>
<title>cssom-view - scroll-behavior: smooth</title>
<meta name="timeout" content="long">
<link rel="help" href="https://drafts.csswg.org/cssom-view/#smooth-scrolling">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/dom/events/scrolling/scroll_support.js"></script>
<style>
  .filler { height: 10000px }

  .smooth {
    scroll-behavior: smooth;
  }

  #scrollable {
    overflow: scroll;
    width: 100px;
    height: 100px;
  }
</style>
<div id="testContainer">
  <div id="scrollable">
    <div class="filler"></div>
  </div>
  <div class="filler"></div>
</div>
<script>
  promise_test(async () => {
    await waitForCompositorReady();
  }, "Make sure the page is ready for animation.");

  var instantHistoryNavigationTest =
    async_test("Instant scrolling while doing history navigation.");
  var smoothHistoryNavigationTest =
    async_test("Smooth scrolling while doing history navigation.");

  function instant() {
    document.documentElement.className = "";
    document.body.className = "";
    window.scrollTo(0, 0);
    var p = document.createElement("pre");
    p.textContent = new Array(1000).join("newline\n");
    var a = document.createElement("a");
    a.href = "#";
    a.name = "foo";
    a.textContent = "foo";
    p.appendChild(a);
    document.body.appendChild(p);
    window.onhashchange = function() {
      window.onhashchange = function() {
        instantHistoryNavigationTest.step(function() {
          assert_equals(location.hash, "", "Shouldn't be scrolled to a fragment.");
          assert_equals(window.scrollY, 0, "Should be scrolled to top.");
        });
        p.remove();
        instantHistoryNavigationTest.done();
        smooth();
      }

      instantHistoryNavigationTest.step(function() {
        assert_equals(location.hash, "#foo", "Should be scrolled to a fragment.");
        assert_not_equals(window.scrollY, 0, "Shouldn't be scrolled to top anymore.");
      });
      history.back();
    }

    instantHistoryNavigationTest.step(function() {
      assert_equals(window.scrollY, 0, "Should be scrolled to top.");
      assert_equals(location.hash, "", "Shouldn't be scrolled to a fragment.");
    });
    location.hash = "foo";
  };

  function smooth() {
    document.documentElement.className = "";
    document.body.className = "";
    window.scrollTo(0, 0);
    var p = document.createElement("pre");
    p.textContent = new Array(1000).join("newline\n");
    var a = document.createElement("a");
    a.href = "#";
    a.name = "bar";
    a.textContent = "bar";
    p.appendChild(a);
    document.body.appendChild(p);
    window.onhashchange = function() {
      window.onhashchange = function() {
        smoothHistoryNavigationTest.step(function() {
          assert_equals(location.hash, "", "Shouldn't be scrolled to a fragment.");
          assert_not_equals(window.scrollY, 0, "Shouldn't be scrolled back to top yet.");
        });
        p.remove();
        smoothHistoryNavigationTest.done();
      }

      smoothHistoryNavigationTest.step(function() {
        assert_equals(location.hash, "#bar", "Should be scrolled to a fragment.");
        assert_not_equals(window.scrollY, 0, "Shouldn't be scrolled to top anymore.");
      });
      history.back();
    }

    smoothHistoryNavigationTest.step(function() {
      assert_equals(window.scrollY, 0, "Should be scrolled to top.");
      assert_equals(location.hash, "", "Shouldn't be scrolled to a fragment.");
    });
    location.hash = "bar";
    document.documentElement.className = "smooth";
  };

  testContainer.style.display = "none";

  // Setting location.hash while loading results in a replace load, which we don't want.
  window.onload = () => {
    step_timeout(instant, 0);
  }
</script>