js验证用户名实例

<script language="javascript"  type="text/javascript">
       function checkname()
       {
          var str=document.form1.username.value;
          if(str.length<6||str.length>10)
          {
            document.getElementById("err").innerHTML="<font>用户名长度错误！</font>";
            document.form1.username.focus();
          }
          else
          {
             document.getElementById("err").innerHTML="";
          }
       }
</script>

 

 

 <form id="form1" name="form1" method="post" action="">
2   <label>
3   用户名：
4   <input type="text" name="username"  onblur="checkname()"/><span id="err"></span>
5   </label>
6 </form>