var elem = document.getElementById("myvideo");
if (elem.requestFullscreen) {
 elem.requestFullscreen();  //IE浏览器
} else if (elem.mozRequestFullScreen) {
 elem.mozRequestFullScreen();   //火狐浏览器
} else if (elem.webkitRequestFullscreen) {
 elem.webkitRequestFullscreen();   //谷歌浏览器
}

function toggleFullScreen() {
 if (!document.fullscreenElement &&  // alternative standard method
   !document.mozFullScreenElement && !document.webkitFullscreenElement) { // current working methods
  if (document.documentElement.requestFullscreen) {
   document.documentElement.requestFullscreen();
  } else if (document.documentElement.mozRequestFullScreen) {
   document.documentElement.mozRequestFullScreen();
  } else if (document.documentElement.webkitRequestFullscreen) {
   document.documentElement.webkitRequestFullscreen(Element.ALLOW_KEYBOARD_INPUT);
  }
 } else {
  if (document.cancelFullScreen) {
   document.cancelFullScreen();
  } else if (document.mozCancelFullScreen) {
   document.mozCancelFullScreen();
  } else if (document.webkitCancelFullScreen) {
   document.webkitCancelFullScreen();
  }
 }
}