​x
 
<!DOCTYPE html>
<html>
<body>
​
<form id="myForm">
  电子邮件：<input type="email" id="myEmail">
</form>
​
<p>单击该按钮可显示电子邮件字段所属表单的 ID。</p>
​
<button onclick="myFunction()">试一试</button>
​
<p id="demo"></p>
​
<script>
function myFunction() {
  var x = document.getElementById("myEmail").form.id;
  document.getElementById("demo").innerHTML = x;
}
</script>
​
</body>
</html>
​