Tryit Editor v2.9

Edit This Code:
<!DOCTYPE html>
<html>
<body>

<form id="myForm" oninput="x.value=parseInt(a.value)+parseInt(b.value)">0
  <input type="range" id="a" value="50">100
  +<input type="number" id="b" value="50">
  =<output id="myOutput" name="x" for="a b"></output>
</form>

<p>Click the button to display the id of the form the output element belongs to.</p>

<p><strong>Note:</strong> The output element is not supported in Internet Explorer.</p>

<button type="button" onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
    var x = document.getElementById("myOutput").form.id;
    document.getElementById("demo").innerHTML = x;
}
</script>

</body>
</html>