js 控制浏览器全屏显示

<html>
<head>
    <script>
        function enterFullscreen() {
            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(docElm.msRequestFullscreen) {
                docElm.msRequestFullscreen();
            }
        }
        function exitFullscreen() {
            //W3C
            if (document.exitFullscreen) {
                document.exitFullscreen();
            }
            //FireFox
            else if (document.mozCancelFullScreen) {
                document.mozCancelFullScreen();
            }
            //Chrome等
            else if (document.webkitCancelFullScreen) {
                document.webkitCancelFullScreen();
            }
            //IE11
            else if (document.msExitFullscreen) {
                document.msExitFullscreen();
            }
        }
    </script>
</head>
<body>
    <h1>测试全屏功能</h1>
    <button onclick="enterFullscreen()">进入全屏</button>
    <button onclick="exitFullscreen()">退出全屏</button>
</body>
</html>