用html5 js实现点击一个按钮达到浏览器全屏效果

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();

}

 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); 

html:-moz-full-screen { 
background: red; 
} 

html:-webkit-full-screen { 
background: red; 
} 

html:fullscreen { 
background: red; 
}