excel单元格时间数值与时间互转

function formatDate(numb, format) {
    var time = new Date((numb - 1) * 24 * 3600000 + 1);
    time.setYear(time.getFullYear() - 70);
    var year = time.getFullYear() + ''
    var month = time.getMonth() + 1 + ''
    var date = time.getDate() + ''
    if (format && format.length === 1) {
        return year + format + month + format + date;
    }
    return year + (month < 10 ? '0' + month : month) + (date < 10 ? '0' + date : date);
}