js提交前弹出提示框

 <form target="_blank" name="f1" method="post" action="sub2.php">
 
 <img style="cursor:pointer;" onClick="b1_onclick()" src="../images/b1.jpg" width="140" height="74">
 
 </form>
 
 <script LANGUAGE="javascript">
 <!--
 function b1_onclick(){
     if(confirm("你确定提交?")){
         document.f1.submit();
         return true;
     }else{
         return false;
     }
     }
     //-->
 </script>