javascript全屏按钮

/*     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";
    }
});