Tryit Editor v2.9

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

<select id="mySelect" size="1">
  <option>Cat</option>
  <option>Dog</option>
  <option>Horse</option>
  <option>Elephant</option>
  <option>Mouse</option>
  <option>Fish</option>
  <option>Cow</option>
</select>

<p>Click the button to change the number of visible options in the dropdown list.</p>

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

<script>
function myFunction() {
     document.getElementById("mySelect").size = "4";
}
</script>

</body>
</html>