<!DOCTYPE html>
<html>
<body>
<form>
<select id="mySelect" size="4">
<option>Apple</option>
<option>Pear</option>
<option>Banana</option>
<option>Orange</option>
</select>
</form>
<p>Click the button to allow multiple selection (meaning that you can select more than one option in the drop-down list).</p>
<button type="button" onclick="myFunction()">Try it</button>
<p><b>Tip:</b> Hold Ctrl or Shift to select more than one option.</p>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("mySelect").multiple = true;
document.getElementById("demo").innerHTML = "You can now select multiple options.";
}
</script>
</body>
</html>