function launchFullscreen(element) {
  if(element.requestFullscreen) {
    element.requestFullscreen();
  } else if(element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if(element.msRequestFullscreen){
    element.msRequestFullscreen();
  } else if(element.webkitRequestFullscreen) {
    element.webkitRequestFullScreen();
  }
}

launchFullscreen(document.documentElement);
launchFullscreen(document.getElementById("videoElement"));

:-webkit-full-screen #myvideo {
  width: 100%;
  height: 100%;
}

function exitFullscreen() {
  if (document.exitFullscreen) {
    document.exitFullscreen();
  } else if (document.msExitFullscreen) {
    document.msExitFullscreen();
  } else if (document.mozCancelFullScreen) {
    document.mozCancelFullScreen();
  } else if (document.webkitExitFullscreen) {
    document.webkitExitFullscreen();
  }
}

exitFullscreen();

var fullscreenElement =
  document.fullscreenElement ||
  document.mozFullScreenElement ||
  document.webkitFullscreenElement;

var fullscreenEnabled =
  document.fullscreenEnabled ||
  document.mozFullScreenEnabled ||
  document.webkitFullscreenEnabled ||
  document.msFullscreenEnabled;

if (fullscreenEnabled) {
  videoElement.requestFullScreen();
} else {
  console.log(‘浏览器当前不能全屏‘);
}

document.addEventListener("fullscreenchange", function( event ) {
  if (document.fullscreenElement) {
    console.log(‘进入全屏‘);
  } else {
    console.log(‘退出全屏‘);
  }
});

:-webkit-full-screen {
  /* properties */
}

:-moz-full-screen {
  /* properties */
}

:-ms-fullscreen {
  /* properties */
}

:full-screen { /*pre-spec */
  /* properties */
}

:fullscreen { /* spec */
  /* properties */
}

/* deeper elements */
:-webkit-full-screen video {
  width: 100%;
  height: 100%;
}

Fullscreen API：全屏操作