JSFiddle - React, Tailwind, and code Playground

HTML

<select id="countrycode" name="countrycode">
        <option value="INT">International</option>
        <option value="USA">USA</option>
        <option value="DE">DE</option>
    </select>
    <div id="us">USA div</div>
    <div id="de">DE div</div>
    <div id="int">INT div</div>

JavaScript

var selectedCountry = '<? echo $p["country"]; ?>';
    //var selectedCountry = 'USA'; // for testing
    var divs = $('#us, #de, #int');
    var selectedCountry = 'USA';
    var countryCodeSelector = $('#countrycode');
    countryCodeSelector.val(selectedCountry);
    selectCountry(selectedCountry);
    countryCodeSelector
        .change(
            function() {
                var code = $(this).val();
                selectCountry(code);
            }
        )
    ;
    function selectCountry(code){
        var selectedID = '';
        switch(code){
            case 'USA':
                selectedID = 'us';
                break;
            case 'DE':
                selectedID = 'de';
                break;
            case 'INT':
                selectedID = 'int';
                break;
        }
        divs.hide();
        $('#' + selectedID).show();
    }