项目分析：

全屏按钮目前js版的大同小异，最大的问题就是无法刷新，刷新就退出。最理想的还是F11。

/*     Fullscreen btn     */
let fullscreen;
let fsEnter = document.getElementById('fullscr');
fsEnter.addEventListener('click', function (e) {
    e.preventDefault();
    if (!fullscreen) {
        fullscreen = true;
        document.documentElement.requestFullscreen();
        fsEnter.innerHTML = "Exit Fullscreen";
    }
    else {
        fullscreen = false;
        document.exitFullscreen();
        fsEnter.innerHTML = "Go Fullscreen";
    }
});

Done !