To find the selected value of a dropdown in JavaScript, do this:
const value = dropdown.value
.For example, if this is your dropdown:
<select id="dropdown">
<option value="1">A</option>
<option value="2">B</option>
<option value="3">C</option>
</select>
Then you can get its value with this JavaScript:
const value = document.getElementById('dropdown').value;