js浏览器全屏的是实现

项目里面有一个须要实现浏览器全屏 也就是F11的效果主流的浏览器都支持  可恶的IE9如下不支持！！！！$("#fullscreen").bind("click",function () {     if($("#fullscreen").text() == "全屏显示"){         var a = document.documentElement;         //W3C         if (a.requestFullscreen) {             a.requestFullscreen();         }         //FireFox         else if (a.mozRequestFullScreen) {             a.mozRequestFullScreen();         }         //Chrome等         else if (a.webkitRequestFullScreen) {             a.webkitRequestFullScreen();         }         //IE11         else if (a.msRequestFullscreen) {             a.msRequestFullscreen();         }         $("#fullscreen").text("关闭全屏");     }else if($("#fullscreen").text() =='关闭全屏' ){         if (document.exitFullscreen) {             document.exitFullscreen();         }         else if (document.mozCancelFullScreen) {             document.mozCancelFullScreen();         }         else if (document.webkitCancelFullScreen) {             document.webkitCancelFullScreen();         }         else if (document.msExitFullscreen) {             document.msExitFullscreen();         }         $("#fullscreen").text('全屏显示')     }})