JSFiddle - React, Tailwind, and code Playground

HTML

<select id="my_alert_type_id" size="2" name="my_alert[type_id]">
    <option value="1">Live</option>
    <option value="2">EOD</option>
</select>
<br>
<br>
<select id="my_alert_category_id" name="myalert[category_id]" size="10">
    <option>select a feed type</option>
</select>

JavaScript

$(function () {
    $('#my_alert_type_id').change(function () {

        var selectedoption = $("#my_alert_type_id").val();
        alert(selectedoption);


        if (selectedoption == "1") {
            $('#my_alert_category_id')
                .find('option')
                .remove()
                .end()
                .append('<option value="1">OPTION1!</option>');

        } else if (selectedoption == "2") {
            $('#my_alert_category_id')
                .find('option')
                .remove()
                .end()
                .append('<option value="2">option2!</option>');


        }
    });

});