<script src="jquery.js" type="text/javascript"></script>
<script src="jquery.viewport.js" type="text/javascript"></script>

$( ":in-viewport" );
$( ":above-the-viewport" );
$( ":below-the-viewport" );
$( ":left-of-viewport" );
$( ":right-of-viewport" );
$( ":partly-above-the-viewport" );
$( ":partly-below-the-viewport" );
$( ":partly-left-of-viewport" );
$( ":partly-right-of-viewport" );
$( ":have-scroll" );

  var wodBackButton = function () {
    //元素在屏幕左側(cè)顯示返回按鈕
    $("#wodsHome:left-of-screen").each(function () {
      $('#wodBackButton').removeClass('hide');
      return;
    });
    //元素在屏幕顯示區(qū)域隱藏返回按鈕
    $("#wodsHome:in-viewport").each(function () {
      $('#wodBackButton').addClass('hide');
      return;
    });
  }

  $('#mediaContainer').bind("scroll", function (event) {
    wodBackButton();
  });

  wodBackButton();