表單驗證....??

請教一下,text欄位若沒輸入值即顯示提醒視窗...
狀況1:沒輸入值,點圖片,正常
狀況2:沒輸入值,按Enter鍵,異常!!(為何提示視窗會彈出兩次?)

<%@ page contentType="text/html; charset=UTF-8" %>

<html>

<head>

</head>

<body>

<%

	String a = null;

	a = request.getParameter("keyword");

	out.println(a);

%>

<script language="javascript">

	function test() {

		if( document.formt.keyword.value == "" ) {

			alert("請輸入值");

			return false;

		} else {

			return true;

		}

	}

</script>

<form name="formt" method="POST" action="/member/test.jsp" onsubmit="return test()">

	輸入:<input name="keyword" size="20" value="" type="text" onkeypress="if ( event.keyCode == 13 ) test();">	

		 <a href="javascript:void(test())"><img src="/images/searchgame.gif" width="68" height="20" align="absmiddle"></a>

</form>

</body>

</html>

1.onkeypress會再按下Enter時執行一次test()，此外，按下Enter對瀏覽器而言等同於要求submit表單，於是表單被送出
2.onsubmit會在表單送出時執行一次test()

andowson wrote:按下Enter對瀏覽器而言等同於要求submit表單，於是表單被送出

成功了,上面這句話點醒我.....謝謝指導!!

輸入:<input name="keyword" size="20" value="" type="text" onkeyDown="if( event.keyCode == 13 && document.formt.keyword.value == '') { alert('請輸入值');return false;} else {return true;}">