<!DOCTYPE html>
<html>
<body>
<form id="myForm">
<input type="week" id="myWeek">
</form>
<p>Click the button to return the id of the form the week field belongs to.</p>
<button onclick="myFunction()">Try it</button>
<p><strong>Note:</strong> input elements with type="week" are not supported in Internet Explorer or Firefox.</p>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myWeek").form.id;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>