jq动态创建多个元素及class

jq动态创建多个元素及class

$("#btn").on("click",function(e){
           
        var num=1;
           
        var str="<div class='clas-"+num+"'>"+
                     "<div class='a1'>"+num+"</div>"+
                     "<div class='a2'></div>"+
                     "<span class='add'></span>"+
                 "</div>";   
         $("#box").append(str); 
    });