js annual meeting lottery program

$(function(){
         
        var alldata = new Array(<?php echo $img;?>);
        var num = alldata.length - 1;
        var show = $("#show");
        var btn = $("#btn");
        var open = false;
     
        function change(){
            var randomVal = Math.round(Math.random() * num);
            var prizeName = alldata[randomVal];
            show.html("<img  src=&#39;images/"+prizeName+"&#39; / alt="js annual meeting lottery program" >");
        }
         
        function run(){
            if(!open){
                timer=setInterval(change,30);
                btn.removeClass(&#39;start&#39;).addClass(&#39;stop&#39;).text(&#39;停止&#39;);
                open = true;
            }else{
                clearInterval(timer);
                btn.removeClass(&#39;stop&#39;).addClass(&#39;start&#39;).text(&#39;开始抽奖&#39;);
                open = false;
            }
        }
         
        btn.click(function(){run();})
         
    })