Convert Timestamp to ISO standard format(YYYY-MM-DD)

gistfile1.js

function convertTimestamp(timestamp) {
    
    function twoDigits(n) {
        return n < 10 ? '0' + n : '' + n;
    }

    var date = new Date(timestamp);
    var day = twoDigits(date.getDate());
    var month = twoDigits(date.getMonth());
    var year = date.getFullYear();

    return year + "-" + month + "-" + day;
}