jquery阻止表单提交

<form action="" method="post" onSubmit="return confirm();" >
</form>

<script>
function checkCoupon(){
   var tof = true;var max_num=$('#max_num').val();
   var type="^[0-9]*[0-9][0-9]*$";
   var r=new RegExp(type);
   var flag=r.test(max_num);
   if (!flag) {
       tof = false;
       alert("最多绑定数量需为大于等于零的自然数");
    }return tof;
}
</script>