I got this html code:

```
<form id = "xxx">
   <ul>
     <li class = "req" > </li>
     <li class = "req" > </li>
     <li class = "req" > </li>
     <li > </li>    ==================> HOW CAN I ADD A CLASS="req" to this li with jquery
     <li class = "req" > </li>
     ....
    <li class = "req" > </li>
  </ul>
</form>

```

So I rewrite the question: There is one li tag that has not ( class= "req"), how can i add that with jquery?
Thank you