Verifique si se selecciona la opción Seleccionar JavaScript
<select id="dropdown">
<option value="" selected hidden>Select an option</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
<option value="4">Four</option>
<option value="5">Five</option>
</select>
<script>
const dropdown = document.getElementById("dropdown");
// to check the dropdown's value at any time, use dropdown.value
// because I've made a default option with no value, to check if
// a value is selected simply do if (dropdown.value !== "") or
// if (dropdown.value)
dropdown.addEventListener("change", function() {
console.log("Selected option element's value:", dropdown.value);
});
</script>
MattDESTROYER