jquery实现表单验证并阻止非法提交

<script type="text/javascript">
//jQuery代码
function confirm()
{
　　if($("#advice").val().length == 0)
{
　　alert("We can't see your advice. Maybe you should fill the form first.");
　　$("#advice").focus();
　　return false;
}
else if($("#advice").val().length <= 15)
{
　　alert("Your advice should longer than 15 letters.");
　　$("#advice").focus();
　　return false;
}
else
{
　　alert("Thank you for your advice! You will get out reply in 24 hours for advice:\n"+$("#advice").val());
　　return true;
}
}
</script>
<form action="" method="post" onSubmit="return confirm();" >
　　<textarea id="advice" rows="20" cols="50"placeholder="Give us some advice?"></textarea>
　　 <input type="submit"value="Thank you"/>
</form>