<select id="animation">
        <option value="1">动画step动画</option>
        <option value="2">动画progress回调</option>
    </select>
    <a></a>
    <input id="exec" type="button" value="执行动画">
    <script type="text/javascript">
        $("#exec").click(function(){
        var v = $("#animation").val();
        var a = $("#aaron");
        if(v == "1"){
            a.animate(
            { height:'50'},
            {duration:2000,
             step:function(now,fx){
                a.text('高度的改变值：'+now)
             } 
            })
        }
        else if(v == "2"){
             a.animate( 
            {height:'70'},
            {duration:2000,
             progress:function(now,fx){
               a.text('进度'+arguments[1]),
               alert('执行结束');
             }
            })    
        }
    })
    </script>

连续弹出窗口三次，没弹出一次 进度增加一次。怎么能只弹出一次。然后进度直接从0-1。