How to dynamically add and get the style name in jquery

<pre name="code" class="html"><script type="text/javascript" src="http://code.jquery.com/jquery-latest.js"></script> 
<select class="form-control" id=&#39;selectId&#39;> 
<option class="all" value="0">全部</option> 
<option class="all" value="1">os2</option> 
<option>os2-anthonos</option> 
<option>os2-apps</option> 
<option>os2-centralpoint</option> 
<option>kf5-experimental</option> 
</select> 
<script> 
 //动态添加option 
 //$("#selectId").append("<option value=&#39;"+value+"&#39;>"+text+"</option>"); 
 $(document).ready(function(){ 
 var string = ""; 
 $("#selectId option").each(function(){ //遍历全部option 
 var text = $(this).text(); //获取option的text 
 var value = $(this).val(); //获取option的value 
 if($(this).attr("class")=="all") 
  string +="{"+text+":"+value+"}"; 
 }); 
 alert(string.substring(0,string.length)); 
}); 
</script>