Web Forms API

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Validation</h2>

<p>Enter a number and click OK:</p>

<input id="id1" type="number" min="100">
<button onclick="myFunction()">OK</button>

<p>If the number is less than 100 (the input's min attribute), an error message will be displayed.</p>

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

<script>
function myFunction() {
  let text;
  if (document.getElementById("id1").validity.rangeUnderflow) {
    text = "Value too small";
  } else {
    text = "Input OK";
  } 
  document.getElementById("demo").innerHTML = text;
}
</script>

</body>
</html>