用javascript鼠标事件做请输入用户名

Question

第四题怎么做啊

Answer 1

<form method="post" action="user.html" id="f">
	<p><img src="1.jpg" width="18" height="18" alt="" /><input type="text" name="name" id="name" oninput="sh(this,'nameinfo')"/></p>
	<p><span id="nameinfo">用户名不能为空</span></p>
	<p><img src="1.jpg" width="18" height="18" alt="" /><input type="password" name="password" id="password" /></p>
</form>
<script type="text/javascript">
function sh(t,id) {
	if (t.value=="")
		document.getElementById(id).style.display = "";
	else
		document.getElementById(id).style.display = "none";
}
</script>