JSFiddle - React, Tailwind, and code Playground

HTML

<select id="countries">
    <option val="USA">USA</option>
    <option val="Canada">Canada</option>
    <option val="Australia">Australia</option>
</select>

<select id="cities">
    <option val="Vancouver">Vancouver</option>
    <option val="New York">New York</option>
</select>

JavaScript

// initially hide the cities
$('#cities').hide();

$("#countries").change(function() {
    // find the selected country
    var selectedCountry = $(this).val();
    // if US or Canada
    if(selectedCountry == "USA" || selectedCountry == "Canada") {
        // show the cities list
        $("#cities").show();
    }
    // otherwise hide it
    else {
        $("#cities").hide();
    }
});

// if US or Canada is the already selected option, then
// cities should show up rightaway
$('#countries').trigger('change');