一行代码实现F11的功能，即让浏览器窗口全屏

//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();
}

//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();
}