<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 () {    //元素在屏幕左側顯示返回按鈕    $("#wodsHome:left-of-screen").each(function () {      $('#wodBackButton').removeClass('hide');      return;    });    //元素在屏幕顯示區域隱藏返回按鈕    $("#wodsHome:in-viewport").each(function () {      $('#wodBackButton').addClass('hide');      return;    });  }  $('#mediaContainer').bind("scroll", function (event) {    wodBackButton();  });  wodBackButton();