Manipulate date formatting

DateTest.js

function main(value) {
    // Add a fake date since we're just working with time
    const epoch = '1970-01-01';
    
    // Convert the given time to a Date Object
    dateVal = new Date(`${epoch} ${value}`);
    
    // Manually determine the suffix for "am" or "pm" since I have found no support in JS
    ampm = (dateVal.getHours() - 12 < 0) ? 'am' : 'pm';
    
    // And manually adjust the time to a 12 hour system
    if (ampm == 'pm') {
        dateVal.setHours(dateVal.getHours() - 12);
    }

    // There must be a better way to format the time of a Date Object...
    // something like return Date(dateVal, "hh:mm:ss");
    //return `${dateVal.getHours()}:${dateVal.getMinutes()}:${dateVal.getSeconds()} ${ampm}`;

    // Use the built in TimeString, but format to use our "am" or "pm" system instead
    return dateVal.toTimeString().replace(/\s.*/, ' ') + ampm;
}

// Test the main function
console.log(main("09:00:00") == "09:00:00 am");
console.log(main("21:00:00") == "09:00:00 pm");