<form>
  <select id="mySelect">
    <option value="option1">Option 1</option>
    <option value="option2">Option 2</option>
    <option value="option3">Option 3</option>
  </select>
  <button onclick="getSelectedValue()">Get Selected Value</button>
</form>

<script>
function getSelectedValue() {
  var selectElement = document.getElementById("mySelect");
  var selectedValue = selectElement.value;
  alert("Selected value: " + selectedValue);
}
</script>