Преобразование даты в unix timestamp и обратно. JavaScript

function timestamp2date(timestamp) {
    var theDate = new Date(timestamp * 1000);
    return theDate.toGMTString();
}

function timestamp2date(timestamp) {
    var theDate = new Date(timestamp * 1000);
    return theDate.toLocaleString();
}

function date2timestamp(year, month, day, hour, min, sec) {
    return (Date.UTC(year, month-1, day, hour, min, sec) / 1000);
}