需求是這樣的 ，有一個圖示元素，點選後進入全屏，再次點選退出全屏。
實現程式碼：

<li id="fullscreen"><a href="#" ><span class="glyphicon glyphicon-resize-full "></span></a></li>

 //控制全屏
    function enterfullscreen() {//進入全屏
        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
 
 exitfullscreen() { //退出全屏
        if (document.exitFullscreen) {
            document.exitFullscreen();
        }
        else if (document.mozCancelFullScreen) {
            document.mozCancelFullScreen();
        }
        else if (document.webkitCancelFullScreen) {
            document.webkitCancelFullScreen();
        }
        else
 
 if (document.msExitFullscreen) {
            document.msExitFullscreen();
        }
    }

    var a=0;
    $('#fullscreen').on('click',function () {
        a++;
        a%2==1?enterfullscreen():exitfullscreen();
    })