fullscreen/api/shadowroot-fullscreen-element.html

<!doctype html>
<html>
<head>
    <title>shadowRoot.fullscreenElement works correctly</title>
    <link rel="author" title="Tim Nguyen" href="https://github.com/nt1m">
    <link rel="help" href="https://fullscreen.spec.whatwg.org/#dom-document-fullscreenelement">
</head>
<div id="host">
    <button onclick="document.exitFullscreen()" id="exitButton">Exit fullscreen</button>
</div>
<button id="requestButton">Go fullscreen</button>

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script>
promise_test(async function() {
    let host = document.getElementById("host");
    host.attachShadow({ mode: "open" }).innerHTML = `
        <style>
        #outer { width: 200px; height: 200px; background: blue }
        </style>
        <div id="outer">
        <slot></slot>
        </div>
    `;
    let outer = host.shadowRoot.querySelector("#outer");
    await new Promise((resolve) => {
        addEventListener("fullscreenchange", resolve, { once: true });
        requestButton.addEventListener("click", () => outer.requestFullscreen());
        test_driver.click(requestButton);
    });

    assert_equals(outer.getRootNode().fullscreenElement, outer, "Correct shadowRoot.fullscreenElement after entering");
    assert_equals(document.fullscreenElement, host, "Correct document.fullscreenElement after entering");

    await new Promise((resolve) => {
        addEventListener("fullscreenchange", resolve, { once: true });
        test_driver.click(exitButton);
    });

    assert_equals(outer.getRootNode().fullscreenElement, null, "Correct shadowRoot.fullscreenElement after exiting");
    assert_equals(document.fullscreenElement, null, "Correct document.fullscreenElement after exiting");
}, "shadowRoot.fullscreenElement works correctly");
</script>
</html>