Js 实现全屏

<input id="Button1" type="button" value="开始全屏" onclick="kaishi()" />
<input id="Button2" type="button" value="关闭全屏" onclick="guanbi()" />

<script>
    function kaishi()
    {
        var docElm = document.documentElement;
        //W3C
        if (docElm.requestFullscreen) {
            docElm.requestFullscreen();
        }
            //FireFox
        else if (docElm.mozRequestFullScreen) {
            docElm.mozRequestFullScreen();
        }
            //Chrome等
        else if (docElm.webkitRequestFullScreen) {
            docElm.webkitRequestFullScreen();
        }
            //IE11
        else if (elem.msRequestFullscreen) {
            elem.msRequestFullscreen();
        }
    }

    function guanbi() {

        if (document.exitFullscreen) {
            document.exitFullscreen();
        }
        else if (document.mozCancelFullScreen) {
            document.mozCancelFullScreen();
        }
        else if (document.webkitCancelFullScreen) {
            document.webkitCancelFullScreen();
        }
        else if (document.msExitFullscreen) {
            document.msExitFullscreen();
        }
    }

    document.addEventListener("fullscreenchange", function () {

        fullscreenState.innerHTML = (document.fullscreen) ? "" : "not ";
    }, false);

    document.addEventListener("mozfullscreenchange", function () {

        fullscreenState.innerHTML = (document.mozFullScreen) ? "" : "not ";
    }, false);

    document.addEventListener("webkitfullscreenchange", function () {

        fullscreenState.innerHTML = (document.webkitIsFullScreen) ? "" : "not ";
    }, false);

    document.addEventListener("msfullscreenchange", function () {

        fullscreenState.innerHTML = (document.msFullscreenElement) ? "" : "not ";
    }, false);
</script>