To preselect a dropdown item using JavaScript, use the selectedIndex property. Add an index of what item you want to be selected.
Dropdown item list is created in HTML using the <select> tag. For JavaScript, we use the <script> tag. Here, under the <script> tag, add_select_id is the id of the <select> tag, whereas add_item_index is the index in numbers. This index is the list item index; you need to add for the item you want to be preselected.
Example
You can try to run the following code to preselect dropdown using JavaScript programmatically −
<!DOCTYPE html>
<html>
<head>
<title>HTML select tag</title>
</head>
<body>
<p> Select any one:</p>
<form>
<select id="dropdown" name="dropdown" class="form-control">
<option value = "Android">Android</option>
<option value = "CSS">CSS</option>
<option value = "Python">Python</option>
</select>
</form>
<script>
document.getElementById("dropdown").selectedIndex = "1";
</script>
</body>
</html>