<p>Select a new car from the list.</p>

<select id="mySelect" onchange="myFunction()">
  <option value="Audi">Audi
  <option value="BMW">BMW
  <option value="Mercedes">Mercedes
  <option value="Volvo">Volvo
</select>

<p>When you select a new car, a function is triggered which outputs the value of the selected car.</p>

<p id="demo"></p>

<script>
function myFunction() {
  let x = document.getElementById("mySelect").value;
  document.getElementById("demo").innerHTML = "You selected: " + x;
}
</script>

<p>Modify the text in the input field, then click outside the field to fire the onchange event.</p>

Enter some text: <input type="text" name="txt" value="Hello" onchange="myFunction(this.value)">

<script>
function myFunction(val) {
  alert("The input value has changed. The new value is: " + val);
}
</script>