Javascript Date object wrong for January 1, 1980

function formatDate(inputDateString) {
    const date = new Date(inputDateString);
            
    // Check if the date is valid
    if (isNaN(date.getTime())) {
        return "Invalid Date";
    }

    const month = String(date.getMonth() + 1).padStart(2, "0"); // Adding 1 because months are zero-based
    const day = String(date.getDate()).padStart(2, "0");
    const year = date.getFullYear();

    return `${month}/${day}/${year}`;
}

var testDate = formatDate("1980-01-01");
console.log("testDate: " + testDate);