How do I format a date in JavaScript?

var monthNames = [
  "January", "February", "March", "April", "May", "June", "July",
  "August", "September", "October", "November", "December"
];
var dayOfWeekNames = [
  "Sunday", "Monday", "Tuesday",
  "Wednesday", "Thursday", "Friday", "Saturday"
];
function formatDate(date, patternStr){
    if (!patternStr) {
        patternStr = 'M/d/yyyy';
    }
    var day = date.getDate(),
        month = date.getMonth(),
        year = date.getFullYear(),
        hour = date.getHours(),
        minute = date.getMinutes(),
        second = date.getSeconds(),
        miliseconds = date.getMilliseconds(),
        h = hour % 12,
        hh = twoDigitPad(h),
        HH = twoDigitPad(hour),
        mm = twoDigitPad(minute),
        ss = twoDigitPad(second),
        aaa = hour < 12 ? 'AM' : 'PM',
        EEEE = dayOfWeekNames[date.getDay()],
        EEE = EEEE.substr(0, 3),
        dd = twoDigitPad(day),
        M = month + 1,
        MM = twoDigitPad(M),
        MMMM = monthNames[month],
        MMM = MMMM.substr(0, 3),
        yyyy = year + "",
        yy = yyyy.substr(2, 2)
    ;
    // checks to see if month name will be used
    patternStr = patternStr
      .replace('hh', hh).replace('h', h)
      .replace('HH', HH).replace('H', hour)
      .replace('mm', mm).replace('m', minute)
      .replace('ss', ss).replace('s', second)
      .replace('S', miliseconds)
      .replace('dd', dd).replace('d', day)
      
      .replace('EEEE', EEEE).replace('EEE', EEE)
      .replace('yyyy', yyyy)
      .replace('yy', yy)
      .replace('aaa', aaa);
    if (patternStr.indexOf('MMM') > -1) {
        patternStr = patternStr
          .replace('MMMM', MMMM)
          .replace('MMM', MMM);
    }
    else {
        patternStr = patternStr
          .replace('MM', MM)
          .replace('M', M);
    }
    return patternStr;
}
function twoDigitPad(num) {
    return num < 10 ? "0" + num : num;
}
console.log(formatDate(new Date()));
console.log(formatDate(new Date(), 'dd-MMM-yyyy')); //OP's request
console.log(formatDate(new Date(), 'EEEE, MMMM d, yyyy HH:mm:ss.S aaa'));
console.log(formatDate(new Date(), 'EEE, MMM d, yyyy HH:mm'));
console.log(formatDate(new Date(), 'yyyy-MM-dd HH:mm:ss.S'));
console.log(formatDate(new Date(), 'M/dd/yyyy h:mmaaa'));

var d = new Date();

var options = {   
    day: 'numeric',
    month: 'long', 
    year: 'numeric'
};

console.log(d.toLocaleDateString('en-ZA', options));

new Date().toLocaleDateString()

// "3/21/2018"

var date = Date.now();
const formatedDate = dayjs(date).format("YYYY-MM-DD")
console.log(formatedDate);

<script src="https://cdnjs.cloudflare.com/ajax/libs/dayjs/1.8.16/dayjs.min.js" crossorigin="anonymous"></script>

const dateToString = d => `${d.getFullYear()}-${('00' + (d.getMonth() + 1)).slice(-2)}-${('00' + d.getDate()).slice(-2)}` 

// how to use:
const myDate = new Date(Date.parse('04 Dec 1995 00:12:00 GMT'))
console.log(dateToString(myDate)) // 1995-12-04

const d = new Date('2010/08/05 23:45') // 26.3.2020
const dtfUK = new Intl.DateTimeFormat('UK', { year: 'numeric', month: '2-digit', day: '2-digit',
        hour: '2-digit',minute: '2-digit', second: '2-digit' }); //
const dtfUS = new Intl.DateTimeFormat('en', { year: 'numeric', month: '2-digit', day: '2-digit',
        hour: '2-digit',minute: '2-digit', second: '2-digit' }); //
console.log(dtfUS.format(d)); // 08/05/2010 11:45:00 PM
console.log(dtfUK.format(d)); // 05.08.2010 23:45:00
/* node.js:
08/05/2010, 11:45:00 PM
2010-08-05 23:45:00
*/

var d = new Date('2010-08-10T10:34:56.789Z');
var str = d.toDateString() + // Tue Aug 10 2010
    ' ' + d.toTimeString().split(' ')[0] + // 12:34:56, GMT+0x00 (GMT+0x:00)
    ' ' + (d.getMonth() + 101) + // 108
    ' ' + d.getMilliseconds(); // 789
console.log(str); // Tue Aug 10 2010 12:34:56 108 789
console.log(//   $1 Tue  $2 Aug  $3 11     $4 2020 $5 12   $6 34   $7 56    $8 108  $9 789
    str.replace(/(\S{3}) (\S{3}) (\d{1,2}) (\d{4}) (\d{2}):(\d{2}):(\d{2}) 1(\d{2}) (\d{1,3})/, '$3-$2-$4 $5:$6.$9 ($1)')
); // 10-Aug-2010 12:34.789 (Tue)
/*
$1: Tue  Week Day string
$2: Aug  Month short text
$3: 11   Day
$4: 2010 Year
$5: 12   Hour
$6: 34   Minute
$7: 56   Seconds
$8: 08   Month
$9: 789  Milliseconds
*/

console.log(
    (function (frm, d) { return [d.toDateString(), d.toTimeString().split(' ')[0], (d.getMonth() + 101), d.getMilliseconds()].join(' ').replace(/(\S{3}) (\S{3}) (\d{1,2}) (\d{4}) (\d{2}):(\d{2}):(\d{2}) 1(\d{2}) (\d{1,3})/, frm); })
    ('$4/$8/$3 $5:$6 ($1)', new Date())
);

let format= d=> d.toString().replace(/\w+ (\w+) (\d+) (\d+).*/,'$2-$1-$3');

console.log( format(Date()) );

let format= (d,a=d.toString().split` `)=> a[2]+"-"+a[1]+"-"+a[3];

console.log( format(Date()) );

const date = new Date("2010-08-10");

let d=new Intl.DateTimeFormat('en-GB',{year:"numeric", month:"short",day:"2-digit"}).format(date).split(" ").join("-");

console.log(d);

var DateFormatter = {
  monthNames: [
    "January", "February", "March", "April", "May", "June",
    "July", "August", "September", "October", "November", "December"
  ],
  dayNames: ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"],
  formatDate: function (date, format) {
    var self = this;
    format = self.getProperDigits(format, /d+/gi, date.getDate());
    format = self.getProperDigits(format, /M+/g, date.getMonth() + 1);
    format = format.replace(/y+/gi, function (y) {
      var len = y.length;
      var year = date.getFullYear();
      if (len == 2)
        return (year + "").slice(-2);
      else if (len == 4)
        return year;
      return y;
    })
    format = self.getProperDigits(format, /H+/g, date.getHours());
    format = self.getProperDigits(format, /h+/g, self.getHours12(date.getHours()));
    format = self.getProperDigits(format, /m+/g, date.getMinutes());
    format = self.getProperDigits(format, /s+/gi, date.getSeconds());
    format = format.replace(/a/ig, function (a) {
      var amPm = self.getAmPm(date.getHours())
      if (a === 'A')
        return amPm.toUpperCase();
      return amPm;
    })
    format = self.getFullOr3Letters(format, /d+/gi, self.dayNames, date.getDay())
    format = self.getFullOr3Letters(format, /M+/g, self.monthNames, date.getMonth())
    return format;
  },
  getProperDigits: function (format, regex, value) {
    return format.replace(regex, function (m) {
      var length = m.length;
      if (length == 1)
        return value;
      else if (length == 2)
        return ('0' + value).slice(-2);
      return m;
    })
  },
  getHours12: function (hours) {
    // https://stackoverflow.com/questions/10556879/changing-the-1-24-hour-to-1-12-hour-for-the-gethours-method
    return (hours + 24) % 12 || 12;
  },
  getAmPm: function (hours) {
    // https://stackoverflow.com/questions/8888491/how-do-you-display-javascript-datetime-in-12-hour-am-pm-format
    return hours >= 12 ? 'pm' : 'am';
  },
  getFullOr3Letters: function (format, regex, nameArray, value) {
    return format.replace(regex, function (s) {
      var len = s.length;
      if (len == 3)
        return nameArray[value].substr(0, 3);
      else if (len == 4)
        return nameArray[value];
      return s;
    })
  }
}

console.log(DateFormatter.formatDate(new Date(), 'YYYY-MM-DD HH:mm:ss'));
console.log(DateFormatter.formatDate(new Date(), 'D DD DDD DDDD, M MM MMM MMMM, YY YYYY, h hh H HH, m mm, s ss, a A'));
console.log(DateFormatter.formatDate(new Date(2005, 1, 2, 3, 4, 5), 'D DD DDD DDDD, M MM MMM MMMM, YY YYYY, h hh H HH, m mm, s ss, a A'));

function formatDate(date) {
    var monthNames = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
    var day = date.getDate(), monthIndex = date.getMonth(), year = date.getFullYear().toString().substr(-2);
    return day + ' ' + monthNames[monthIndex] + ' ' + year;
}

document.write(formatDate(new Date()));

var monthNames = [
  "January", "February", "March", "April", "May", "June", "July",
  "August", "September", "October", "November", "December"
];
var dayOfWeekNames = [
  "Sunday", "Monday", "Tuesday",
  "Wednesday", "Thursday", "Friday", "Saturday"
];
function formatDate(date, formatStr){
    if (!formatStr) {
      formatStr = 'dd/mm/yyyy';
    }
    var day = date.getDate(),
        month = date.getMonth(),
        year = date.getFullYear(),
        hour = date.getHours(),
        minute = date.getMinutes(),
        second = date.getSeconds(),
        miliseconds = date.getMilliseconds(),
        hh = twoDigitPad(hour),
        mm = twoDigitPad(minute),
        ss = twoDigitPad(second),
        EEEE = dayOfWeekNames[date.getDay()],
        EEE = EEEE.substr(0, 3),
        dd = twoDigitPad(day),
        M = month + 1,
        MM = twoDigitPad(M),
        MMMM = monthNames[month],
        MMM = MMMM.substr(0, 3),
        yyyy = year + "",
        yy = yyyy.substr(2, 2)
    ;
    return formatStr
      .replace('hh', hh).replace('h', hour)
      .replace('mm', mm).replace('m', minute)
      .replace('ss', ss).replace('s', second)
      .replace('S', miliseconds)
      .replace('dd', dd).replace('d', day)
      .replace('MMMM', MMMM).replace('MMM', MMM).replace('MM', MM).replace('M', M)
      .replace('EEEE', EEEE).replace('EEE', EEE)
      .replace('yyyy', yyyy)
      .replace('yy', yy)
    ;
}
function twoDigitPad(num) {
    return num < 10 ? "0" + num : num;
}
console.log(formatDate(new Date()));
console.log(formatDate(new Date(), 'EEEE, MMMM d, yyyy hh:mm:ss:S'));
console.log(formatDate(new Date(), 'EEE, MMM d, yyyy hh:mm'));
console.log(formatDate(new Date(), 'yyyy-MM-dd hh:mm:ss:S'));
console.log(formatDate(new Date(), 'yy-MM-dd hh:mm'));

function formatWith(formatStr, date, opts) {

    if (!date) {
        date = new Date();
    }

    opts = opts || {};

    let _days = opts.days;

    if (!_days) {
        _days = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];
    }

    let _months = opts.months;

    if (!_months) {
        _months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];
    }

    const pad = (number, strDigits, isUnpad) => {
        const strNum = number.toString();
        if (!isUnpad && strNum.length > strDigits.length) {
            return strNum;
        } else {
            return ('0000' + strNum).slice(-strDigits.length);
        }
    };

    const timezone = (date, letter) => {
        const chunk = [];
        const offset = -date.getTimezoneOffset();
        chunk.push(offset === 0 ? 'Z' : offset > 0 ? '+' : '-');//add Z or +,-
        if (offset === 0) return chunk;
        chunk.push(pad(Math.floor(offset / 60), '00'));//hour
        if (letter === 'X') return chunk.join('');
        if (letter === 'XXX') chunk.push(':');
        chunk.push(pad((offset % 60), '00'));//min
        return chunk.join('');
    };

    const ESCAPE_DELIM = '\0';
    const escapeStack = [];

    const escapedFmtStr = formatStr.replace(/'.*?'/g, m => {
        escapeStack.push(m.replace(/'/g, ''));
        return ESCAPE_DELIM + (escapeStack.length - 1) + ESCAPE_DELIM;
    });

    const formattedStr = escapedFmtStr
        .replace(/y{4}|y{2}/g, m => pad(date.getFullYear(), m, true))
        .replace(/M{3}/g, m => _months[date.getMonth()])
        .replace(/M{1,2}/g, m => pad(date.getMonth() + 1, m))
        .replace(/M{1,2}/g, m => pad(date.getMonth() + 1, m))
        .replace(/d{1,2}/g, m => pad(date.getDate(), m))
        .replace(/H{1,2}/g, m => pad(date.getHours(), m))
        .replace(/h{1,2}/g, m => {
            const hours = date.getHours();
            return pad(hours === 0 ? 12 : hours > 12 ? hours - 12 : hours, m);
        })
        .replace(/a{1,2}/g, m => date.getHours() >= 12 ? 'PM' : 'AM')
        .replace(/m{1,2}/g, m => pad(date.getMinutes(), m))
        .replace(/s{1,2}/g, m => pad(date.getSeconds(), m))
        .replace(/S{3}/g, m => pad(date.getMilliseconds(), m))
        .replace(/[E]+/g, m => _days[date.getDay()])
        .replace(/[Z]+/g, m => timezone(date, m))
        .replace(/X{1,3}/g, m => timezone(date, m))
    ;

    const unescapedStr = formattedStr.replace(/\0\d+\0/g, m => {
        const unescaped = escapeStack.shift();
        return unescaped.length > 0 ? unescaped : '\'';
    });

    return unescapedStr;
}

// Let's format with above function
const dateStr = '2018/07/17 12:08:56';
const date = new Date(dateStr);
const patterns = [
    "dd-MMM-yyyy",
    "yyyyMMdd'T'HHmmssXX",//ISO8601
    "yyyy-MM-dd'T'HH:mm:ssXXX",//ISO8601EX
    "E, dd MMM yyyy HH:mm:ss Z",//RFC1123(RFC822) like email
    "yyyy.MM.dd 'at' hh:mm:ss Z",//hh shows 1-12
    "EEE, MMM d, ''yy",
    "h:mm a",
    "hh 'o''''clock' a, X",
];

for (let pattern of patterns) {
    console.log(`${pattern} → ${formatWith(pattern, date)}`);
}

const MONTHS = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sept', 'Oct', 'Nov', 'Dec']

const date = new Date()

const dateString = `${date.getDate()}-${MONTHS[date.getMonth()]}-${date.getFullYear()}`

console.log(dateString)

const formatDate = date => {
const d = new Date(date)
let month = (d.getMonth() + 1).toString()
let day = d.getDate().toString()
const year = d.getFullYear()
if (month.length < 2) {
    month = '0' + month
}
if (day.length < 2) {
    day = '0' + day
}
return [ year, month, day ].join('-')
}

console.log(formatDate('01/07/2022'))

function convert_month(i = 0, option = "num") { // i = index

  var object_months = [
    { num: 01, short: "Jan", long: "January" },
    { num: 02, short: "Feb", long: "Februari" }, 
    { num: 03, short: "Mar", long: "March" },          
    { num: 04, short: "Apr", long: "April" },
    { num: 05, short: "May", long: "May" },
    { num: 06, short: "Jun", long: "Juni" },
    { num: 07, short: "Jul", long: "July" },
    { num: 08, short: "Aug", long: "August" },
    { num: 09, short: "Sep", long: "September" },
    { num: 10, short: "Oct", long: "October" },
    { num: 11, short: "Nov", long: "November" },
    { num: 12, short: "Dec", long: "December" }
  ];
        
  return object_months[i][option];

}
      
var d = new Date();
      
// https://stackoverflow.com/questions/1408289/how-can-i-do-string-interpolation-in-javascript
var num   = `${d.getDate()}-${convert_month(d.getMonth())}-${d.getFullYear()}`;
var short = `${d.getDate()}-${convert_month(d.getMonth(), "short")}-${d.getFullYear()}`;
var long  = `${d.getDate()}-${convert_month(d.getMonth(), "long")}-${d.getFullYear()}`;

document.querySelector("#num").innerHTML = num;
document.querySelector("#short").innerHTML = short;
document.querySelector("#long").innerHTML = long;

<p>Numeric  : <span id="num"></span> (default)</p>
<p>Short    : <span id="short"></span></p>
<p>Long     : <span id="long"></span></p>

// format_date(date, pattern, utc)
// - date
//   - a JavaScript Date object
//   - use "new Date()" for current time
// - pattern
//   - a string with embedded {codes} like
//     "{year4}-{month02}-{day02}: {dayname3}"
//     see format_date_funcs below for complete list
//   - any other letters go through unchanged
// - utc
//   - if true, shows date in UTC time "zone"
//   - if false/omitted, shows date in local time zone
//
var month_names =
[
  "January", "February", "March", "April", "May", "June", "July",
  "August", "September", "October", "November", "December"
];
var day_of_week_names =
[
  "Sunday", "Monday", "Tuesday",
  "Wednesday", "Thursday", "Friday", "Saturday"
];

function space_pad2(num)
{
    return num < 10 ? " " + num : num;
}

function zero_pad2(num)
{
    return num < 10 ? "0" + num : num;
}

function space_pad3(num)
{
    if (num < 10)
        return "  " + num;
    else if (num < 100)
        return " " + num;
    else
        return num;
}

function zero_pad3(num)
{
    if (num < 10)
        return "00" + num;
    else if (num < 100)
        return "0" + num;
    else
        return num;
}

var format_date_funcs =
{
    // {year4}  = '1902'
    // {year02} =   '02'
    //
    'year4': function(date, utc)
    {
        var year = utc ? date.getUTCFullYear() : date.getFullYear();
        return year;
    },
    'year02': function(date, utc)
    {
        var year = utc ? date.getUTCFullYear() : date.getFullYear();
        return year.toString().substr(2,2);
    },
    // {month}   =  '1' - '12'
    // {month2}  = ' 1' - '12' (space padded)
    // {month02} = '01' - '12'
    //
    'month': function(date, utc)
    {
        var month = utc ? date.getUTCMonth() : date.getMonth(); // [0,11]
        return            month + 1;
    },
    'month2': function(date, utc)
    {
        var month = utc ? date.getUTCMonth() : date.getMonth(); // [0,11]
        return space_pad2(month + 1);
    },
    'month02': function(date, utc)
    {
        var month = utc ? date.getUTCMonth() : date.getMonth(); // [0,11]
        return zero_pad2(month + 1);
    },
    // {monthname}  = 'January'
    // {monthname3} = 'Jan'
    //
    'monthname': function(date, utc)
    {
        var month = utc ? date.getUTCMonth() : date.getMonth(); // [0,11]
        return month_names[month];
    },
    'monthname3': function(date, utc)
    {
        var month = utc ? date.getUTCMonth() : date.getMonth(); // [0,11]
        return month_names[month].substr(0, 3);
    },
    // {day}   =  '1' - '31'
    // {day2}  = ' 1' - '31' (space padded)
    // {day02} = '01' - '31'
    //
    'day': function(date, utc)
    {
        var date = utc ? date.getUTCDate() : date.getDate(); // [1,31]
        return date;
    },
    'day2': function(date, utc)
    {
        var date = utc ? date.getUTCDate() : date.getDate(); // [1,31]
        return space_pad2(date);
    },
    'day02': function(date, utc)
    {
        var date = utc ? date.getUTCDate() : date.getDate(); // [1,31]
        return zero_pad2(date);
    },
    // {dayname}  = 'Tuesday'
    // {dayname3} = 'Tue'
    //
    'dayname': function(date, utc)
    {
        var day = utc ? date.getUTCDay() : date.getDay(); // [0,6]
        return day_of_week_names[day];
    },
    'dayname3': function(date, utc)
    {
        var day = utc ? date.getUTCDay() : date.getDay(); // [0,6]
        return day_of_week_names[day].substr(0,3);
    },
    // {24hour}   =  '0' - '23'
    // {24hour2}  = ' 0' - '23' (space padded)
    // {24hour02} = '00' - '23'
    //
    '24hour': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        return hour;
    },
    '24hour2': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        return space_pad2(hour);
    },
    '24hour02': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        return zero_pad2(hour);
    },
    // {12hour}   =  '1' - '12'
    // {12hour2}  = ' 1' - '12' (space padded)
    // {12hour02} = '01' - '12'
    // {ampm}     = 'am' or 'pm'
    // {AMPM}     = 'AM' or 'PM'
    //
    '12hour': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        hour = hour % 12; // [0,11]
        if (0 === hour) hour = 12;
        return hour;
    },
    '12hour2': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        hour = hour % 12; // [0,11]
        if (0 === hour) hour = 12;
        return space_pad2(hour);
    },
    '12hour02': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        hour = hour % 12; // [0,11]
        if (0 === hour) hour = 12;
        return zero_pad2(hour);
    },
    'ampm': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        return (hour < 12 ? 'am' : 'pm');
    },
    'AMPM': function(date, utc)
    {
        var hour = utc ? date.getUTCHours() : date.getHours(); // [0,23]
        return (hour < 12 ? 'AM' : 'PM');
    },
    // {minute}   =  '0' - '59'
    // {minute2}  = ' 0' - '59' (space padded)
    // {minute02} = '00' - '59'
    //
    'minute': function(date, utc)
    {
        var minute = utc ? date.getUTCMinutes() : date.getMinutes(); // [0,59]
        return minute;
    },
    'minute2': function(date, utc)
    {
        var minute = utc ? date.getUTCMinutes() : date.getMinutes(); // [0,59]
        return space_pad2(minute);
    },
    'minute02': function(date, utc)
    {
        var minute = utc ? date.getUTCMinutes() : date.getMinutes(); // [0,59]
        return zero_pad2(minute);
    },
    // {second}   =  '0' - '59'
    // {second2}  = ' 0' - '59' (space padded)
    // {second02} = '00' - '59'
    //
    'second': function(date, utc)
    {
        var second = utc ? date.getUTCSeconds() : date.getSeconds(); // [0,59]
        return second;
    },
    'second2': function(date, utc)
    {
        var second = utc ? date.getUTCSeconds() : date.getSeconds(); // [0,59]
        return space_pad2(second);
    },
    'second02': function(date, utc)
    {
        var second = utc ? date.getUTCSeconds() : date.getSeconds(); // [0,59]
        return zero_pad2(second);
    },
    // {msec}   =   '0' - '999'
    // {msec3}  = '  0' - '999' (space padded)
    // {msec03} = '000' - '999'
    //
    'msec': function(date, utc)
    {
        var msec =
            utc ? date.getUTCMilliseconds() : date.getMilliseconds(); // [0,999]
        return msec;
    },
    'msec3': function(date, utc)
    {
        var msec =
            utc ? date.getUTCMilliseconds() : date.getMilliseconds(); // [0,999]
        return space_pad3(msec);
    },
    'msec03': function(date, utc)
    {
        var msec =
            utc ? date.getUTCMilliseconds() : date.getMilliseconds(); // [0,999]
        return zero_pad3(msec);
    },
    // {open} = '{' (in case you actually want '{' in the output)
    //
    'open': function(date, utc)
    {
        return '{';
    },
    // {close} = '}' (in case you actually want '}' in the output)
    //
    'close': function(date, utc)
    {
        return '}';
    },
};

function format_date(date, pattern, utc)
{
    if (!pattern)
    {
        pattern = '{month}/{day}/{year4}';
    }

    var ret = '';

    while (pattern.length > 0)
    {
        var s = pattern.indexOf('{');
        var e = pattern.indexOf('}');
        //console.log('s ' + s + ' e ' + e);
        if (-1 !== s && -1 !== e && s < e)
        {
            // - there is a well-formed {foo} in range [s,e]
            // - first we emit range [0,s) as literal
        }
        else
        {
            // - rest of string has no {} or has malformed }{ or { or }
            // - just emit the rest of the string as literal and be done
            s = pattern.length;
        }
        // emit range [0,s) as literal
        if (s > 0)
        {
            ret += pattern.substr(0, s);
            pattern = pattern.substr(s);
            e -= s;
            s = 0;
        }

        if (0 === pattern.length) break;

        // emit range [s=0,e] by evaluating code
        console.assert(0 === s); // position of {
        console.assert(e > 0);  // position of }
        console.assert('{' === pattern.substr(s, 1));
        console.assert('}' === pattern.substr(e, 1));
        var code = pattern.substr(1,e-1);
        var func = format_date_funcs[code];
        console.assert(func);
        ret += func(date, utc);

        pattern = pattern.substr(e+1);
    }

    return ret;
}

if (1) // test format_date
{
    var fmt = '[';
    for (var func in format_date_funcs)
    {
        if (!format_date_funcs.hasOwnProperty(func)) continue;
        fmt += '{' + func + '}/';
    }
    fmt += ']';
    var now = new Date();
    console.log(fmt);
    console.log(format_date(now, fmt, false /* utc */));
    console.log(format_date(now, fmt, true /* utc */));
}