<html>
<head>
<script>
function displayResult()
{
var x=document.getElementById("email").form.id;
alert(x);
}
</script>
</head>
<body>
<form id="form1">
Email: <input type="text" id="email" value="someone@example.com">
</form>
<button type="button" onclick="displayResult()">显示容器表单的id</button>
</body>
</html>