onclick进入全屏

var elem = document.getElementById("myvideo");    if (elem.requestFullscreen) {      elem.requestFullscreen();    } else if (elem.msRequestFullscreen) {      elem.msRequestFullscreen();    } else if (elem.mozRequestFullScreen) {      elem.mozRequestFullScreen();    } else if (elem.webkitRequestFullscreen) {      elem.webkitRequestFullscreen();    }