navigation-api/navigate-event/intercept-navigation-back.html

<!doctype html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
async_test(t => {
  let start_length = navigation.entries().length;
  let start_index = navigation.currentEntry.index;

  // Wait for after the load event so that the navigation doesn't get converted
  // into a replace navigation.
  window.onload = () => t.step_timeout(() => {
    navigation.navigate("#foo").committed.then(() => {
      assert_true(navigation.canGoBack);
      navigation.onnavigate = t.step_func(e => e.intercept());
      navigation.back().committed.then(t.step_func_done(() => {
        assert_equals(navigation.entries().length, start_length + 1);
        assert_equals(navigation.currentEntry, navigation.entries()[start_index]);
      }));
    });
  }, 0);
}, "event.intercept() can intercept navigation.back()");
</script>