//控制全屏
function enterfullscreen() { //进入全屏
  $("#fullscreen").html("退出全屏");
  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();
  }
}
 
function exitfullscreen() { //退出全屏
  $("#fullscreen").html("切换全屏");
  if(document.exitFullscreen) {
    document.exitFullscreen();
  } else if(document.mozCancelFullScreen) {
    document.mozCancelFullScreen();
  } else if(document.webkitCancelFullScreen) {
    document.webkitCancelFullScreen();
  } else if(document.msExitFullscreen) {
    document.msExitFullscreen();
  }
}
 
var a = 0;
$('#fullscreen').on('click', function() {
  a++;
  a % 2 == 1 ? enterfullscreen() : exitfullscreen();
})

<a type="button" id="fullscreen" class="btn btn-default visible-lg visible-md"><i class="fa fa-refresh" aria-hidden="true"></i> 切换全屏</a>