不同浏览器全屏方案

/* 获取(<video>)元素 */
var elem = document.getElementsByTagName("video")[0];

/* 全屏查看 */
function openFullscreen() {
  if (elem.requestFullscreen) {
     elem.requestFullscreen();
  } else if (elem.mozRequestFullScreen) {/* Firefox */
     elem.mozRequestFullScreen();
  } else if (elem.webkitRequestFullscreen) { /* Chrome, Safari and Opera */
     elem.webkitRequestFullscreen();
  } else if (elem.msRequestFullscreen) { /* IE/Edge */
     elem.msRequestFullscreen();
  }
}