Tryit Editor v2.9

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

<form>
<select id="mySelect">
  <option>Cats</option>
  <option>Dogs</option>
</select>
</form>

<p>Click the button to disable the dropdown list.</p>

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

<script>
function myFunction() {
    document.getElementById("mySelect").disabled = true;
}
</script>

</body>
</html>