jQuery.fn.countDown = function(settings,to) {
  settings = jQuery.extend({
    startFontSize: '36px',
    endFontSize: '12px',
    duration: 1000,
    startNumber: 10,
    endNumber: 0,
    callBack: function() { }
  }, settings);
  return this.each(function() {
    //where do we start?
    if(!to && to != settings.endNumber) { to = settings.startNumber; }
    //set the countdown to the starting number
    $(this).text(to).css('fontSize',settings.startFontSize);
    //loopage
    $(this).animate({
      'fontSize': settings.endFontSize
    },settings.duration,'',function() {
      if(to > settings.endNumber + 1) {
        $(this).css('fontSize',settings.startFontSize).text(to - 1).
 countDown(settings,to - 1);
      }
      else
      {
        settings.callBack(this);
      }
    });
  });
};
/* sample usage
//调用方法
//
$('#countdown').countDown({
  startNumber: 10,
  callBack: function(me) {
    $(me).text('倒计时加载完毕').css('color','#090');
  }
});