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<script charset="utf-8" id="seajsnode"src="http://static.alipayobjects.com/seajs/??seajs/2.2.2/sea.js,seajs-combo/1.0.1/seajs-combo.js,seajs-style/1.0.2/seajs-style.js"></script>

  seajs.config({
    base: 'http://static.alipayobjects.com',
    alias: {
      'jquery': 'jquery/1.7.2/jquery',
      'position': 'position/1.1.0/index'
    }
  });
  seajs.use(['jquery', 'position'], function($, Position){
    var stop = false;
    var target = $('<div class="target"></div>')
      .hover(function(){stop = true;},function(){stop = false;})
      .appendTo(document.body);
    setInterval(function() {
      if (stop) return;
      var x = Math.floor(Math.random() * 100);
      var y = Math.floor(Math.random() * 100);
      Position.pin(
        { element: target, x: 'center', y: 'center' }, 
        { element: Position.VIEWPORT, x: x + '%', y: y + '%' }
      );
    }, 800);
  });

.target{width:50px;height:50px;border-radius:25px;background:#000;transition:All 1s ease;-webkit-transition:All 1s ease;-moz-transition:All 1s ease;}