main.js

let elem = document.querySelector(".lockscreen");
function screenLock() {
    elem.classList.add("lock")
    elem.classList.remove("unlock")
    if (elem.requestFullscreen) {
        elem.requestFullscreen();
    } else if (elem.webkitRequestFullscreen) {
        elem.webkitRequestFullscreen();
    } else if (elem.msRequestFullscreen) {
        elem.msRequestFullscreen();
    }
}
function screenUnlock() {
    elem.classList.add("unlock")
    elem.classList.remove("lock")
    setTimeout(() => {
        if (document.exitFullscreen) {
            document.exitFullscreen();
          } else if (document.webkitExitFullscreen) {
            document.webkitExitFullscreen();
          } else if (document.msExitFullscreen) {
            document.msExitFullscreen();
          }
    }, 1000);
}