PHPの日付形式をJavascriptの日付形式に変換する関数（日付自体ではありません！）

// Parser and formatter using PHP tokens
let P = function(global) {

  let P = {lang: 'en-GB'};

  // Format tokens and functions
  let tokens = {
  
    // DAY
    // day of month, pad to 2 digits
    d: d => pad(d.getDate()),
    // Day name, first 3 letters
    D: d => getDayName(d).substr(0,3),
    // day of month, no padding
    j: d => d.getDate(),
    // Full day name
    l: d => getDayName(d),
    // ISO weekday number (1 = Monday ... 7 = Sunday)
    N: d => d.getDay() || 7,
    // Ordinal suffix for day of the month
    S: d => getOrdinal(d.getDate()),
    // Weekday number (0 = Sunday, 6 = Saturday)
    w: d => d.getDay(),
    // Day of year, 1 Jan is 0
    z: d => {
      let Y = d.getFullYear(),
          M = d.getMonth(),
          D = d.getDate();
      return Math.floor((Date.UTC(Y, M, D) - Date.UTC(Y, 0, 1)) / 8.64e7) ;
    },
    // ISO week number of year
    W: d => getWeekNumber(d)[1],
    // Full month name
    F: d => getMonthName(d),
    // Month number, padded
    m: d => pad(d.getMonth() + 1),
    // 3 letter month name
    M: d => getMonthName(d).substr(0, 3),
    // Month number, no pading
    n: d => d.getMonth() + 1,
    // Days in month
    t: d => new Date(d.getFullYear(), d.getMonth() + 1, 0).getDate(),
    // Return 1 if d is a leap year, otherwise 0
    L: d => new Date(d.getFullYear(), 1, 29).getDate() == 29? 1 : 0,
    // ISO week numbering year
    o: d => getWeekNumber(d)[0],
    // 4 digit year
    Y: d => {
      let year = d.getFullYear();
      if (year < 0) {
        year = '-' + ('000' + Math.abs(year)).slice(-4);
      }
      return year;
    },
    // 2 digit year
    y: d => {
      let year = d.getFullYear();
      if (year >= 0) {
        return ('0' + year).slice(-2);
      } else {
        year = Math.abs(year);
        return - + ('0' + year).slice(-2);
      }
    },
    // Lowercase am or pm
    a: d => d.getHours() < 12? 'am' : 'pm',
    // Uppercase AM or PM
    A: d => d.getHours() < 12? 'AM' : 'PM',
    // Swatch internet time
    B: d => (((+d + 3.6e6) % 8.64e7) / 8.64e4).toFixed(0),
    // 12 hour hour no padding
    g: d => (d.getHours() % 12) || 12,
    // 24 hour hour no padding
    G: d => d.getHours(),
    // 12 hour hour padded
    h: d => pad((d.getHours() % 12) || 12),
    // 24 hour hour padded
    H: d => pad(d.getHours()),
    // Minutes padded
    i: d => pad(d.getMinutes()),
    // Seconds padded
    s: d => pad(d.getSeconds()),
    // Microseconds padded - always returns 000000
    u: d => '000000',
    // Milliseconds
    v: d => padd(d.getMilliseconds()),
    // Timezone identifier: UTC, GMT or IANA Tz database identifier - Not supported
    e: d => void 0,
    // If in daylight saving: 1 yes, 0 no
    I: d => d.getTimezoneOffset() == getOffsets(d)[0]? 0 : 1,
    // Difference to GMT in hours, e.g. +0200
    O: d => minsToHours(-d.getTimezoneOffset(), false),
    // Difference to GMT in hours with colon, e.g. +02:00
    P: d => minsToHours(-d.getTimezoneOffset(), true),
    // Timezone abbreviation, e.g. AEST. Dodgy but may work…
    T: d => d.toLocaleString('en',{year:'numeric',timeZoneName:'long'}).replace(/[^A-Z]/g, ''),
    // Timezone offset in seconds, +ve east
    Z: d => d.getTimezoneOffset() * -60,
    
    // ISO 8601 format - UTC
    // c: d => d.getUTCFullYear() + '-' + pad(d.getUTCMonth() + 1) + '-' + pad(d.getUTCDate()) +
    //        'T' + pad(d.getUTCHours()) + ':' + pad(d.getUTCMinutes()) + ':' + pad(d.getUTCSeconds()) +
    //        '+00:00',
    
    // ISO 8601 format - local
    c: d => P.format(d, 'Y-m-d\\TH:i:sP'),
    // RFC 2822 formatted date, local timezone
    r: d => P.format(d, 'D, d M Y H:i:s O'),
    // Seconds since UNIX epoch (same as ECMAScript epoch)
    U: d => d.getTime() / 1000 | 0
  };
  
  // Helpers
  // Return day name for date
  let getDayName = d => d.toLocaleString(P.lang, {weekday:'long'});
  // Return month name for date
  let getMonthName = d => d.toLocaleString(P.lang, {month:'long'});
  // Return [std offest, DST offset]. If no DST, same offset for both
  let getOffsets = d => {
    let y = d.getFullYear();
    let offsets = [0, 2, 5, 9].map(m => new Date(y, m).getTimezoneOffset());
    return [Math.max(...offsets), Math.min(...offsets)];
  }  
  // Return ordinal for positive integer
  let getOrdinal = n => {
    n = n % 100;
    let ords = ['th','st','nd','rd'];
    return (n < 10 || n > 13) ? ords[n%10] || 'th' : 'th';
  };
  // Return ISO week number and year
  let getWeekNumber = d => {
    let e = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
    e.setUTCDate(e.getUTCDate() + 4 - (e.getUTCDay()||7));
    var yearStart = new Date(Date.UTC(e.getUTCFullYear(),0,1));
    var weekNo = Math.ceil(( ( (e - yearStart) / 86400000) + 1)/7);
    return [e.getUTCFullYear(), weekNo];
  };
  // Return true if o is a Date, otherwise false
  let isDate = o => Object.prototype.toString.call(o) == '[object Date]';
  // Convert numeric minutes to +/-HHMM or +/-HH:MM
  let minsToHours = (mins, colon) => {
    let sign = mins < 0? '-' : '+';
    mins = Math.abs(mins);
    let H = pad(mins / 60 | 0);
    let M = pad(mins % 60);
    return sign + H + (colon? ':' : '') + M;
  };
  // Pad single digits with a leading zero
  let pad = n => (n < 10? '0' : '') + n;
  // Pad single digits with two leading zeros, double digits with one leading zero
  let padd = n => (n < 10? '00' : n < 100? '0' : '') + n;
  // To be completed...
  let parse = s => 'not complete';

  P.parse = parse;
  
  // Format date using token string s
  function format(date, s) {
    // Minimal input validation
    if (!isDate(date) || typeof s != 'string') {
      return; // undefined
    }

    return s.split('').reduce((acc, c, i, chars) => {
      // Add quoted characters to output
      if (c == '\\') {
        acc += chars.splice(i+1, 1);
      // If character matches a token, use it
      } else if (c in tokens) {
        acc += tokens[c](date);
      // Otherwise, just add character to output
      } else {
        acc += c;
      }
      return acc;
    }, '');
  }
  P.format = format;
  
  return P;
}(this);


// Examples
console.log('Today is ' + P.format(new Date(), 'l, jS \\o\\f F, Y'));
let startPWars = new Date(-431,3,25);
let endPWars   = new Date(-404,0);
console.log('The Peloponnesian Wars started on ' + 
  P.format(startPWars, 'd F, Y') +
  ' and ended in ' +
  P.format(endPWars, 'Y'));

function showDate() {
  let format = document.getElementById('i0').value;
  document.getElementById('sp0').textContent = P.format(new Date(), format) || 'invalid tokens';
}

<input id="i0" placeholder="PHP format, e.g. d-M-Y">
<button onclick="showDate()">Show formatted date</button>
<br>
<span id="sp0"></span>