<!doctype html>
<body>
<select id="genres">
<option value="rock">Rock</option>
<option value="blues" selected>Blues</option>
</select>
<script>
// 1)
let selectedOption = genres.options[genres.selectedIndex];
// 2)
let newOption = new Option("Classic", "classic", true, true);
genres.append(newOption);
// 3)
</script>
</body>
defaultSelected Optional
A Boolean that sets the selected attribute value, i.e. so that this will be the default value selected in the element when the page is first loaded. If this is not specified, a default value of false is used. Note that a value of true does not set the option to selected if it is not already selected.
Простой
Простой
Средний