vanillajs-datepicker/dist/js/datepicker.js

A vanilla JavaScript remake of bootstrap-datepicker for Bulma and other CSS frameworks

var Datepicker = (function () {
  'use strict';

  function lastItemOf(arr) {
    return arr[arr.length - 1];
  }

  // push only the items not included in the array
  function pushUnique(arr, ...items) {
    items.forEach((item) => {
      if (arr.includes(item)) {
        return;
      }
      arr.push(item);
    });
    return arr;
  }

  function stringToArray(str, separator) {
    // convert empty string to an empty array
    return str ? str.split(separator) : [];
  }

  function isInRange(testVal, min, max) {
    const minOK = min === undefined || testVal >= min;
    const maxOK = max === undefined || testVal <= max;
    return minOK && maxOK;
  }

  function limitToRange(val, min, max) {
    if (val < min) {
      return min;
    }
    if (val > max) {
      return max;
    }
    return val;
  }

  function createTagRepeat(tagName, repeat, attributes = {}, index = 0, html = '') {
    const openTagSrc = Object.keys(attributes).reduce((src, attr) => {
      let val = attributes[attr];
      if (typeof val === 'function') {
        val = val(index);
      }
      return `${src} ${attr}="${val}"`;
    }, tagName);
    html += `<${openTagSrc}></${tagName}>`;

    const next = index + 1;
    return next < repeat
      ? createTagRepeat(tagName, repeat, attributes, next, html)
      : html;
  }

  // Remove the spacing surrounding tags for HTML parser not to create text nodes
  // before/after elements
  function optimizeTemplateHTML(html) {
    return html.replace(/>\s+/g, '>').replace(/\s+</, '<');
  }

  function stripTime(timeValue) {
    return new Date(timeValue).setHours(0, 0, 0, 0);
  }

  function today() {
    return new Date().setHours(0, 0, 0, 0);
  }

  // Get the time value of the start of given date or year, month and day
  function dateValue(...args) {
    switch (args.length) {
      case 0:
        return today();
      case 1:
        return stripTime(args[0]);
    }

    // use setFullYear() to keep 2-digit year from being mapped to 1900-1999
    const newDate = new Date(0);
    newDate.setFullYear(...args);
    return newDate.setHours(0, 0, 0, 0);
  }

  function addDays(date, amount) {
    const newDate = new Date(date);
    return newDate.setDate(newDate.getDate() + amount);
  }

  function addWeeks(date, amount) {
    return addDays(date, amount * 7);
  }

  function addMonths(date, amount) {
    // If the day of the date is not in the new month, the last day of the new
    // month will be returned. e.g. Jan 31 + 1 month → Feb 28 (not Mar 03)
    const newDate = new Date(date);
    const monthsToSet = newDate.getMonth() + amount;
    let expectedMonth = monthsToSet % 12;
    if (expectedMonth < 0) {
      expectedMonth += 12;
    }

    const time = newDate.setMonth(monthsToSet);
    return newDate.getMonth() !== expectedMonth ? newDate.setDate(0) : time;
  }

  function addYears(date, amount) {
    // If the date is Feb 29 and the new year is not a leap year, Feb 28 of the
    // new year will be returned.
    const newDate = new Date(date);
    const expectedMonth = newDate.getMonth();
    const time = newDate.setFullYear(newDate.getFullYear() + amount);
    return expectedMonth === 1 && newDate.getMonth() === 2 ? newDate.setDate(0) : time;
  }

  // Calculate the distance bettwen 2 days of the week
  function dayDiff(day, from) {
    return (day - from + 7) % 7;
  }

  // Get the date of the specified day of the week of given base date
  function dayOfTheWeekOf(baseDate, dayOfWeek, weekStart = 0) {
    const baseDay = new Date(baseDate).getDay();
    return addDays(baseDate, dayDiff(dayOfWeek, weekStart) - dayDiff(baseDay, weekStart));
  }

  function calcWeekNum(dayOfTheWeek, sameDayOfFirstWeek) {
    return Math.round((dayOfTheWeek - sameDayOfFirstWeek) / 604800000) + 1;
  }

  // Get the ISO week number of a date
  function getIsoWeek(date) {
    // - Start of ISO week is Monday
    // - Use Thursday for culculation because the first Thursday of ISO week is
    //   always in January
    const thuOfTheWeek = dayOfTheWeekOf(date, 4, 1);
    // - Week 1 in ISO week is the week including Jan 04
    // - Use the Thu of given date's week (instead of given date itself) to
    //   calculate week 1 of the year so that Jan 01 - 03 won't be miscalculated
    //   as week 0 when Jan 04 is Mon - Wed
    const firstThu = dayOfTheWeekOf(new Date(thuOfTheWeek).setMonth(0, 4), 4, 1);
    // return Math.round((thuOfTheWeek - firstThu) / 604800000) + 1;
    return calcWeekNum(thuOfTheWeek, firstThu);
  }

  // Calculate week number in traditional week number system
  // @see https://en.wikipedia.org/wiki/Week#Other_week_numbering_systems
  function calcTraditionalWeekNumber(date, weekStart) {
    // - Week 1 of traditional week is the week including the Jan 01
    // - Use Jan 01 of given date's year to calculate the start of week 1
    const startOfFirstWeek = dayOfTheWeekOf(new Date(date).setMonth(0, 1), weekStart, weekStart);
    const startOfTheWeek = dayOfTheWeekOf(date, weekStart, weekStart);
    const weekNum = calcWeekNum(startOfTheWeek, startOfFirstWeek);
    if (weekNum < 53) {
      return weekNum;
    }
    // If the 53rd week includes Jan 01, it's actually next year's week 1
    const weekOneOfNextYear = dayOfTheWeekOf(new Date(date).setDate(32), weekStart, weekStart);
    return startOfTheWeek === weekOneOfNextYear ? 1 : weekNum;
  }

  // Get the Western traditional week number of a date
  function getWesternTradWeek(date) {
    // Start of Western traditionl week is Sunday
    return calcTraditionalWeekNumber(date, 0);
  }

  // Get the Middle Eastern week number of a date
  function getMidEasternWeek(date) {
    // Start of Middle Eastern week is Saturday
    return calcTraditionalWeekNumber(date, 6);
  }

  // Get the start year of the period of years that includes given date
  // years: length of the year period
  function startOfYearPeriod(date, years) {
    /* @see https://en.wikipedia.org/wiki/Year_zero#ISO_8601 */
    const year = new Date(date).getFullYear();
    return Math.floor(year / years) * years;
  }

  // Convert date to the first/last date of the month/year of the date
  function regularizeDate(date, timeSpan, useLastDate) {
    if (timeSpan !== 1 && timeSpan !== 2) {
      return date;
    }
    const newDate = new Date(date);
    if (timeSpan === 1) {
      useLastDate
        ? newDate.setMonth(newDate.getMonth() + 1, 0)
        : newDate.setDate(1);
    } else {
      useLastDate
        ? newDate.setFullYear(newDate.getFullYear() + 1, 0, 0)
        : newDate.setMonth(0, 1);
    }
    return newDate.setHours(0, 0, 0, 0);
  }

  // pattern for format parts
  const reFormatTokens = /dd?|DD?|mm?|MM?|yy?(?:yy)?/;
  // pattern for non date parts
  const reNonDateParts = /[\s!-/:-@[-`{-~年月日]+/;
  // cache for persed formats
  let knownFormats = {};
  // parse funtions for date parts
  const parseFns = {
    y(date, year) {
      return new Date(date).setFullYear(parseInt(year, 10));
    },
    m(date, month, locale) {
      const newDate = new Date(date);
      let monthIndex = parseInt(month, 10) - 1;

      if (isNaN(monthIndex)) {
        if (!month) {
          return NaN;
        }

        const monthName = month.toLowerCase();
        const compareNames = name => name.toLowerCase().startsWith(monthName);
        // compare with both short and full names because some locales have periods
        // in the short names (not equal to the first X letters of the full names)
        monthIndex = locale.monthsShort.findIndex(compareNames);
        if (monthIndex < 0) {
          monthIndex = locale.months.findIndex(compareNames);
        }
        if (monthIndex < 0) {
          return NaN;
        }
      }

      newDate.setMonth(monthIndex);
      return newDate.getMonth() !== normalizeMonth(monthIndex)
        ? newDate.setDate(0)
        : newDate.getTime();
    },
    d(date, day) {
      return new Date(date).setDate(parseInt(day, 10));
    },
  };
  // format functions for date parts
  const formatFns = {
    d(date) {
      return date.getDate();
    },
    dd(date) {
      return padZero(date.getDate(), 2);
    },
    D(date, locale) {
      return locale.daysShort[date.getDay()];
    },
    DD(date, locale) {
      return locale.days[date.getDay()];
    },
    m(date) {
      return date.getMonth() + 1;
    },
    mm(date) {
      return padZero(date.getMonth() + 1, 2);
    },
    M(date, locale) {
      return locale.monthsShort[date.getMonth()];
    },
    MM(date, locale) {
      return locale.months[date.getMonth()];
    },
    y(date) {
      return date.getFullYear();
    },
    yy(date) {
      return padZero(date.getFullYear(), 2).slice(-2);
    },
    yyyy(date) {
      return padZero(date.getFullYear(), 4);
    },
  };

  // get month index in normal range (0 - 11) from any number
  function normalizeMonth(monthIndex) {
    return monthIndex > -1 ? monthIndex % 12 : normalizeMonth(monthIndex + 12);
  }

  function padZero(num, length) {
    return num.toString().padStart(length, '0');
  }

  function parseFormatString(format) {
    if (typeof format !== 'string') {
      throw new Error("Invalid date format.");
    }
    if (format in knownFormats) {
      return knownFormats[format];
    }

    // sprit the format string into parts and seprators
    const separators = format.split(reFormatTokens);
    const parts = format.match(new RegExp(reFormatTokens, 'g'));
    if (separators.length === 0 || !parts) {
      throw new Error("Invalid date format.");
    }

    // collect format functions used in the format
    const partFormatters = parts.map(token => formatFns[token]);

    // collect parse function keys used in the format
    // iterate over parseFns' keys in order to keep the order of the keys.
    const partParserKeys = Object.keys(parseFns).reduce((keys, key) => {
      const token = parts.find(part => part[0] !== 'D' && part[0].toLowerCase() === key);
      if (token) {
        keys.push(key);
      }
      return keys;
    }, []);

    return knownFormats[format] = {
      parser(dateStr, locale) {
        const dateParts = dateStr.split(reNonDateParts).reduce((dtParts, part, index) => {
          if (part.length > 0 && parts[index]) {
            const token = parts[index][0];
            if (token === 'M') {
              dtParts.m = part;
            } else if (token !== 'D') {
              dtParts[token] = part;
            }
          }
          return dtParts;
        }, {});

        // iterate over partParserkeys so that the parsing is made in the oder
        // of year, month and day to prevent the day parser from correcting last
        // day of month wrongly
        return partParserKeys.reduce((origDate, key) => {
          const newDate = parseFns[key](origDate, dateParts[key], locale);
          // ingnore the part failed to parse
          return isNaN(newDate) ? origDate : newDate;
        }, today());
      },
      formatter(date, locale) {
        let dateStr = partFormatters.reduce((str, fn, index) => {
          return str += `${separators[index]}${fn(date, locale)}`;
        }, '');
        // separators' length is always parts' length + 1,
        return dateStr += lastItemOf(separators);
      },
    };
  }

  function parseDate(dateStr, format, locale) {
    if (dateStr instanceof Date || typeof dateStr === 'number') {
      const date = stripTime(dateStr);
      return isNaN(date) ? undefined : date;
    }
    if (!dateStr) {
      return undefined;
    }
    if (dateStr === 'today') {
      return today();
    }

    if (format && format.toValue) {
      const date = format.toValue(dateStr, format, locale);
      return isNaN(date) ? undefined : stripTime(date);
    }

    return parseFormatString(format).parser(dateStr, locale);
  }

  function formatDate(date, format, locale) {
    if (isNaN(date) || (!date && date !== 0)) {
      return '';
    }

    const dateObj = typeof date === 'number' ? new Date(date) : date;

    if (format.toDisplay) {
      return format.toDisplay(dateObj, format, locale);
    }

    return parseFormatString(format).formatter(dateObj, locale);
  }

  const range = document.createRange();

  function parseHTML(html) {
    return range.createContextualFragment(html);
  }

  function getParent(el) {
    return el.parentElement
      || (el.parentNode instanceof ShadowRoot ? el.parentNode.host : undefined);
  }

  function isActiveElement(el) {
    return el.getRootNode().activeElement === el;
  }

  function hideElement(el) {
    if (el.style.display === 'none') {
      return;
    }
    // back up the existing display setting in data-style-display
    if (el.style.display) {
      el.dataset.styleDisplay = el.style.display;
    }
    el.style.display = 'none';
  }

  function showElement(el) {
    if (el.style.display !== 'none') {
      return;
    }
    if (el.dataset.styleDisplay) {
      // restore backed-up dispay property
      el.style.display = el.dataset.styleDisplay;
      delete el.dataset.styleDisplay;
    } else {
      el.style.display = '';
    }
  }

  function emptyChildNodes(el) {
    if (el.firstChild) {
      el.removeChild(el.firstChild);
      emptyChildNodes(el);
    }
  }

  function replaceChildNodes(el, newChildNodes) {
    emptyChildNodes(el);
    if (newChildNodes instanceof DocumentFragment) {
      el.appendChild(newChildNodes);
    } else if (typeof newChildNodes === 'string') {
      el.appendChild(parseHTML(newChildNodes));
    } else if (typeof newChildNodes.forEach === 'function') {
      newChildNodes.forEach((node) => {
        el.appendChild(node);
      });
    }
  }

  const listenerRegistry = new WeakMap();
  const {addEventListener, removeEventListener} = EventTarget.prototype;

  // Register event listeners to a key object
  // listeners: array of listener definitions;
  //   - each definition must be a flat array of event target and the arguments
  //     used to call addEventListener() on the target
  function registerListeners(keyObj, listeners) {
    let registered = listenerRegistry.get(keyObj);
    if (!registered) {
      registered = [];
      listenerRegistry.set(keyObj, registered);
    }
    listeners.forEach((listener) => {
      addEventListener.call(...listener);
      registered.push(listener);
    });
  }

  function unregisterListeners(keyObj) {
    let listeners = listenerRegistry.get(keyObj);
    if (!listeners) {
      return;
    }
    listeners.forEach((listener) => {
      removeEventListener.call(...listener);
    });
    listenerRegistry.delete(keyObj);
  }

  // Event.composedPath() polyfill for Edge
  // based on https://gist.github.com/kleinfreund/e9787d73776c0e3750dcfcdc89f100ec
  if (!Event.prototype.composedPath) {
    const getComposedPath = (node, path = []) => {
      path.push(node);

      let parent;
      if (node.parentNode) {
        parent = node.parentNode;
      } else if (node.host) { // ShadowRoot
        parent = node.host;
      } else if (node.defaultView) {  // Document
        parent = node.defaultView;
      }
      return parent ? getComposedPath(parent, path) : path;
    };

    Event.prototype.composedPath = function () {
      return getComposedPath(this.target);
    };
  }

  function findFromPath(path, criteria, currentTarget) {
    const [node, ...rest] = path;
    if (criteria(node)) {
      return node;
    }
    if (node === currentTarget || node.tagName === 'HTML' || rest.length === 0) {
      // stop when reaching currentTarget or <html>
      return;
    }
    return findFromPath(rest, criteria, currentTarget);
  }

  // Search for the actual target of a delegated event
  function findElementInEventPath(ev, selector) {
    const criteria = typeof selector === 'function'
      ? selector
      : el => el instanceof Element && el.matches(selector);
    return findFromPath(ev.composedPath(), criteria, ev.currentTarget);
  }

  // default locales
  const locales = {
    en: {
      days: ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"],
      daysShort: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"],
      daysMin: ["Su", "Mo", "Tu", "We", "Th", "Fr", "Sa"],
      months: ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
      monthsShort: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"],
      today: "Today",
      clear: "Clear",
      titleFormat: "MM y"
    }
  };

  // config options updatable by setOptions() and their default values
  const defaultOptions = {
    autohide: false,
    beforeShowDay: null,
    beforeShowDecade: null,
    beforeShowMonth: null,
    beforeShowYear: null,
    clearButton: false,
    dateDelimiter: ',',
    datesDisabled: [],
    daysOfWeekDisabled: [],
    daysOfWeekHighlighted: [],
    defaultViewDate: undefined, // placeholder, defaults to today() by the program
    disableTouchKeyboard: false,
    enableOnReadonly: true,
    format: 'mm/dd/yyyy',
    language: 'en',
    maxDate: null,
    maxNumberOfDates: 1,
    maxView: 3,
    minDate: null,
    nextArrow: '»',
    orientation: 'auto',
    pickLevel: 0,
    prevArrow: '«',
    showDaysOfWeek: true,
    showOnClick: true,
    showOnFocus: true,
    startView: 0,
    title: '',
    todayButton: false,
    todayButtonMode: 0,
    todayHighlight: false,
    updateOnBlur: true,
    weekNumbers: 0,
    weekStart: 0,
  };

  const {
    language: defaultLang,
    format: defaultFormat,
    weekStart: defaultWeekStart,
  } = defaultOptions;

  // Reducer function to filter out invalid day-of-week from the input
  function sanitizeDOW(dow, day) {
    return dow.length < 6 && day >= 0 && day < 7
      ? pushUnique(dow, day)
      : dow;
  }

  function determineGetWeekMethod(numberingMode, weekStart) {
    const methodId = numberingMode === 4
      ? (weekStart === 6 ? 3 : !weekStart + 1)
      : numberingMode;
    switch (methodId) {
      case 1:
        return getIsoWeek;
      case 2:
        return getWesternTradWeek;
      case 3:
        return getMidEasternWeek;
    }
  }

  function updateWeekStart(newValue, config, weekNumbers) {
    config.weekStart = newValue;
    config.weekEnd = (newValue + 6) % 7;
    if (weekNumbers === 4) {
      config.getWeekNumber = determineGetWeekMethod(4, newValue);
    }
    return newValue;
  }

  // validate input date. if invalid, fallback to the original value
  function validateDate(value, format, locale, origValue) {
    const date = parseDate(value, format, locale);
    return date !== undefined ? date : origValue;
  }

  // Validate viewId. if invalid, fallback to the original value
  function validateViewId(value, origValue, max = 3) {
    const viewId = parseInt(value, 10);
    return viewId >= 0 && viewId <= max ? viewId : origValue;
  }

  function replaceOptions(options, from, to, convert = undefined) {
    if (from in options) {
      if (!(to in options)) {
        options[to] = convert ? convert(options[from]) : options[from];
      }
      delete options[from];
    }
  }

  // Create Datepicker configuration to set
  function processOptions(options, datepicker) {
    const inOpts = Object.assign({}, options);
    const config = {};
    const locales = datepicker.constructor.locales;
    const rangeEnd = !!datepicker.rangeSideIndex;
    let {
      datesDisabled,
      format,
      language,
      locale,
      maxDate,
      maxView,
      minDate,
      pickLevel,
      startView,
      weekNumbers,
      weekStart,
    } = datepicker.config || {};

    // for backword compatibility
    replaceOptions(inOpts, 'calendarWeeks', 'weekNumbers', val => val ? 1 : 0);
    replaceOptions(inOpts, 'clearBtn', 'clearButton');
    replaceOptions(inOpts, 'todayBtn', 'todayButton');
    replaceOptions(inOpts, 'todayBtnMode', 'todayButtonMode');

    if (inOpts.language) {
      let lang;
      if (inOpts.language !== language) {
        if (locales[inOpts.language]) {
          lang = inOpts.language;
        } else {
          // Check if langauge + region tag can fallback to the one without
          // region (e.g. fr-CA → fr)
          lang = inOpts.language.split('-')[0];
          if (!locales[lang]) {
            lang = false;
          }
        }
      }
      delete inOpts.language;
      if (lang) {
        language = config.language = lang;

        // update locale as well when updating language
        const origLocale = locale || locales[defaultLang];
        // use default language's properties for the fallback
        locale = Object.assign({
          format: defaultFormat,
          weekStart: defaultWeekStart
        }, locales[defaultLang]);
        if (language !== defaultLang) {
          Object.assign(locale, locales[language]);
        }
        config.locale = locale;
        // if format and/or weekStart are the same as old locale's defaults,
        // update them to new locale's defaults
        if (format === origLocale.format) {
          format = config.format = locale.format;
        }
        if (weekStart === origLocale.weekStart) {
          weekStart = updateWeekStart(locale.weekStart, config, weekNumbers);
        }
      }
    }

    if (inOpts.format) {
      const hasToDisplay = typeof inOpts.format.toDisplay === 'function';
      const hasToValue = typeof inOpts.format.toValue === 'function';
      const validFormatString = reFormatTokens.test(inOpts.format);
      if ((hasToDisplay && hasToValue) || validFormatString) {
        format = config.format = inOpts.format;
      }
      delete inOpts.format;
    }

    //*** pick level ***//
    let newPickLevel = pickLevel;
    if ('pickLevel' in inOpts) {
      newPickLevel = validateViewId(inOpts.pickLevel, pickLevel, 2);
      delete inOpts.pickLevel;
    }
    if (newPickLevel !== pickLevel) {
      if (newPickLevel > pickLevel) {
        // complement current minDate/madDate so that the existing range will be
        // expanded to fit the new level later
        if (!('minDate' in inOpts)) {
          inOpts.minDate = minDate;
        }
        if (!('maxDate' in inOpts)) {
          inOpts.maxDate = maxDate;
        }
      }
      // complement datesDisabled so that it will be reset later
      if (datesDisabled && !inOpts.datesDisabled) {
        inOpts.datesDisabled = [];
      }
      pickLevel = config.pickLevel = newPickLevel;
    }

    //*** dates ***//
    // while min and maxDate for "no limit" in the options are better to be null
    // (especially when updating), the ones in the config have to be undefined
    // because null is treated as 0 (= unix epoch) when comparing with time value
    let minDt = minDate;
    let maxDt = maxDate;
    if ('minDate' in inOpts) {
      const defaultMinDt = dateValue(0, 0, 1);
      minDt = inOpts.minDate === null
        ? defaultMinDt  // set 0000-01-01 to prevent negative values for year
        : validateDate(inOpts.minDate, format, locale, minDt);
      if (minDt !== defaultMinDt) {
        minDt = regularizeDate(minDt, pickLevel, false);
      }
      delete inOpts.minDate;
    }
    if ('maxDate' in inOpts) {
      maxDt = inOpts.maxDate === null
        ? undefined
        : validateDate(inOpts.maxDate, format, locale, maxDt);
      if (maxDt !== undefined) {
        maxDt = regularizeDate(maxDt, pickLevel, true);
      }
      delete inOpts.maxDate;
    }
    if (maxDt < minDt) {
      minDate = config.minDate = maxDt;
      maxDate = config.maxDate = minDt;
    } else {
      if (minDate !== minDt) {
        minDate = config.minDate = minDt;
      }
      if (maxDate !== maxDt) {
        maxDate = config.maxDate = maxDt;
      }
    }

    if (inOpts.datesDisabled) {
      const dtsDisabled = inOpts.datesDisabled;
      if (typeof dtsDisabled === 'function') {
        config.datesDisabled = null;
        config.checkDisabled = (timeValue, viewId) => dtsDisabled(
          new Date(timeValue),
          viewId,
          rangeEnd
        );
      } else {
        const disabled = config.datesDisabled = dtsDisabled.reduce((dates, dt) => {
          const date = parseDate(dt, format, locale);
          return date !== undefined
            ? pushUnique(dates, regularizeDate(date, pickLevel, rangeEnd))
            : dates;
        }, []);
        config.checkDisabled = timeValue => disabled.includes(timeValue);
      }
      delete inOpts.datesDisabled;
    }
    if ('defaultViewDate' in inOpts) {
      const viewDate = parseDate(inOpts.defaultViewDate, format, locale);
      if (viewDate !== undefined) {
        config.defaultViewDate = viewDate;
      }
      delete inOpts.defaultViewDate;
    }

    //*** days of week ***//
    if ('weekStart' in inOpts) {
      const wkStart = Number(inOpts.weekStart) % 7;
      if (!isNaN(wkStart)) {
        weekStart = updateWeekStart(wkStart, config, weekNumbers);
      }
      delete inOpts.weekStart;
    }
    if (inOpts.daysOfWeekDisabled) {
      config.daysOfWeekDisabled = inOpts.daysOfWeekDisabled.reduce(sanitizeDOW, []);
      delete inOpts.daysOfWeekDisabled;
    }
    if (inOpts.daysOfWeekHighlighted) {
      config.daysOfWeekHighlighted = inOpts.daysOfWeekHighlighted.reduce(sanitizeDOW, []);
      delete inOpts.daysOfWeekHighlighted;
    }

    //*** week numbers ***//
    if ('weekNumbers' in inOpts) {
      let method = inOpts.weekNumbers;
      if (method) {
        const getWeekNumber = typeof method === 'function'
          ? (timeValue, startOfWeek) => method(new Date(timeValue), startOfWeek)
          : determineGetWeekMethod((method = parseInt(method, 10)), weekStart);
        if (getWeekNumber) {
          weekNumbers = config.weekNumbers = method;
          config.getWeekNumber = getWeekNumber;
        }
      } else {
        weekNumbers = config.weekNumbers = 0;
        config.getWeekNumber = null;
      }
      delete inOpts.weekNumbers;
    }

    //*** multi date ***//
    if ('maxNumberOfDates' in inOpts) {
      const maxNumberOfDates = parseInt(inOpts.maxNumberOfDates, 10);
      if (maxNumberOfDates >= 0) {
        config.maxNumberOfDates = maxNumberOfDates;
        config.multidate = maxNumberOfDates !== 1;
      }
      delete inOpts.maxNumberOfDates;
    }
    if (inOpts.dateDelimiter) {
      config.dateDelimiter = String(inOpts.dateDelimiter);
      delete inOpts.dateDelimiter;
    }

    //*** view ***//
    let newMaxView = maxView;
    if ('maxView' in inOpts) {
      newMaxView = validateViewId(inOpts.maxView, maxView);
      delete inOpts.maxView;
    }
    // ensure max view >= pick level
    newMaxView = pickLevel > newMaxView ? pickLevel : newMaxView;
    if (newMaxView !== maxView) {
      maxView = config.maxView = newMaxView;
    }

    let newStartView = startView;
    if ('startView' in inOpts) {
      newStartView = validateViewId(inOpts.startView, newStartView);
      delete inOpts.startView;
    }
    // ensure pick level <= start view <= max view
    if (newStartView < pickLevel) {
      newStartView = pickLevel;
    } else if (newStartView > maxView) {
      newStartView = maxView;
    }
    if (newStartView !== startView) {
      config.startView = newStartView;
    }

    //*** template ***//
    if (inOpts.prevArrow) {
      const prevArrow = parseHTML(inOpts.prevArrow);
      if (prevArrow.childNodes.length > 0) {
        config.prevArrow = prevArrow.childNodes;
      }
      delete inOpts.prevArrow;
    }
    if (inOpts.nextArrow) {
      const nextArrow = parseHTML(inOpts.nextArrow);
      if (nextArrow.childNodes.length > 0) {
        config.nextArrow = nextArrow.childNodes;
      }
      delete inOpts.nextArrow;
    }

    //*** misc ***//
    if ('disableTouchKeyboard' in inOpts) {
      config.disableTouchKeyboard = 'ontouchstart' in document && !!inOpts.disableTouchKeyboard;
      delete inOpts.disableTouchKeyboard;
    }
    if (inOpts.orientation) {
      const orientation = inOpts.orientation.toLowerCase().split(/\s+/g);
      config.orientation = {
        x: orientation.find(x => (x === 'left' || x === 'right')) || 'auto',
        y: orientation.find(y => (y === 'top' || y === 'bottom')) || 'auto',
      };
      delete inOpts.orientation;
    }
    if ('todayButtonMode' in inOpts) {
      switch(inOpts.todayButtonMode) {
        case 0:
        case 1:
          config.todayButtonMode = inOpts.todayButtonMode;
      }
      delete inOpts.todayButtonMode;
    }

    //*** copy the rest ***//
    Object.entries(inOpts).forEach(([key, value]) => {
      if (value !== undefined && key in defaultOptions) {
        config[key] = value;
      }
    });

    return config;
  }

  const defaultShortcutKeys = {
    show: {key: 'ArrowDown'},
    hide: null,
    toggle: {key: 'Escape'},
    prevButton: {key: 'ArrowLeft', ctrlOrMetaKey: true},
    nextButton: {key: 'ArrowRight', ctrlOrMetaKey: true},
    viewSwitch: {key: 'ArrowUp', ctrlOrMetaKey: true},
    clearButton: {key: 'Backspace', ctrlOrMetaKey: true},
    todayButton: {key: '.', ctrlOrMetaKey: true},
    exitEditMode: {key: 'ArrowDown', ctrlOrMetaKey: true},
  };

  function createShortcutKeyConfig(options) {
    return Object.keys(defaultShortcutKeys).reduce((keyDefs, shortcut) => {
      const keyDef = options[shortcut] === undefined
        ? defaultShortcutKeys[shortcut]
        : options[shortcut];
      const key = keyDef && keyDef.key;
      if (!key || typeof key !== 'string') {
        return keyDefs;
      }

      const normalizedDef = {
        key,
        ctrlOrMetaKey: !!(keyDef.ctrlOrMetaKey || keyDef.ctrlKey || keyDef.metaKey),
      };
      if (key.length > 1) {
        normalizedDef.altKey = !!keyDef.altKey;
        normalizedDef.shiftKey = !!keyDef.shiftKey;
      }
      keyDefs[shortcut] = normalizedDef;
      return keyDefs;
    }, {});
  }

  const pickerTemplate = optimizeTemplateHTML(`<div class="datepicker">
  <div class="datepicker-picker">
    <div class="datepicker-header">
      <div class="datepicker-title"></div>
      <div class="datepicker-controls">
        <button type="button" class="%buttonClass% prev-button prev-btn"></button>
        <button type="button" class="%buttonClass% view-switch"></button>
        <button type="button" class="%buttonClass% next-button next-btn"></button>
      </div>
    </div>
    <div class="datepicker-main"></div>
    <div class="datepicker-footer">
      <div class="datepicker-controls">
        <button type="button" class="%buttonClass% today-button today-btn"></button>
        <button type="button" class="%buttonClass% clear-button clear-btn"></button>
      </div>
    </div>
  </div>
</div>`);

  const daysTemplate = optimizeTemplateHTML(`<div class="days">
  <div class="days-of-week">${createTagRepeat('span', 7, {class: 'dow'})}</div>
  <div class="datepicker-grid">${createTagRepeat('span', 42)}</div>
</div>`);

  const weekNumbersTemplate = optimizeTemplateHTML(`<div class="week-numbers calendar-weeks">
  <div class="days-of-week"><span class="dow"></span></div>
  <div class="weeks">${createTagRepeat('span', 6, {class: 'week'})}</div>
</div>`);

  // Base class of the view classes
  class View {
    constructor(picker, config) {
      Object.assign(this, config, {
        picker,
        element: parseHTML(`<div class="datepicker-view"></div>`).firstChild,
        selected: [],
        isRangeEnd: !!picker.datepicker.rangeSideIndex,
      });
      this.init(this.picker.datepicker.config);
    }

    init(options) {
      if ('pickLevel' in options) {
        this.isMinView = this.id === options.pickLevel;
      }
      this.setOptions(options);
      this.updateFocus();
      this.updateSelection();
    }

    prepareForRender(switchLabel, prevButtonDisabled, nextButtonDisabled) {
      // refresh disabled years on every render in order to clear the ones added
      // by beforeShow hook at previous render
      this.disabled = [];

      const picker = this.picker;
      picker.setViewSwitchLabel(switchLabel);
      picker.setPrevButtonDisabled(prevButtonDisabled);
      picker.setNextButtonDisabled(nextButtonDisabled);
    }

    setDisabled(date, classList) {
      classList.add('disabled');
      pushUnique(this.disabled, date);
    }

    // Execute beforeShow() callback and apply the result to the element
    // args:
    performBeforeHook(el, timeValue) {
      let result = this.beforeShow(new Date(timeValue));
      switch (typeof result) {
        case 'boolean':
          result = {enabled: result};
          break;
        case 'string':
          result = {classes: result};
      }

      if (result) {
        const classList = el.classList;
        if (result.enabled === false) {
          this.setDisabled(timeValue, classList);
        }
        if (result.classes) {
          const extraClasses = result.classes.split(/\s+/);
          classList.add(...extraClasses);
          if (extraClasses.includes('disabled')) {
            this.setDisabled(timeValue, classList);
          }
        }
        if (result.content) {
          replaceChildNodes(el, result.content);
        }
      }
    }

    renderCell(el, content, cellVal, date, {selected, range}, outOfScope, extraClasses = []) {
      el.textContent = content;
      if (this.isMinView) {
        el.dataset.date = date;
      }

      const classList = el.classList;
      el.className = `datepicker-cell ${this.cellClass}`;
      if (cellVal < this.first) {
        classList.add('prev');
      } else if (cellVal > this.last) {
        classList.add('next');
      }
      classList.add(...extraClasses);
      if (outOfScope || this.checkDisabled(date, this.id)) {
        this.setDisabled(date, classList);
      }
      if (range) {
        const [rangeStart, rangeEnd] = range;
        if (cellVal > rangeStart && cellVal < rangeEnd) {
          classList.add('range');
        }
        if (cellVal === rangeStart) {
          classList.add('range-start');
        }
        if (cellVal === rangeEnd) {
          classList.add('range-end');
        }
      }
      if (selected.includes(cellVal)) {
        classList.add('selected');
      }
      if (cellVal === this.focused) {
        classList.add('focused');
      }

      if (this.beforeShow) {
        this.performBeforeHook(el, date);
      }
    }

    refreshCell(el, cellVal, selected, [rangeStart, rangeEnd]) {
      const classList = el.classList;
      classList.remove('range', 'range-start', 'range-end', 'selected', 'focused');
      if (cellVal > rangeStart && cellVal < rangeEnd) {
        classList.add('range');
      }
      if (cellVal === rangeStart) {
        classList.add('range-start');
      }
      if (cellVal === rangeEnd) {
        classList.add('range-end');
      }
      if (selected.includes(cellVal)) {
        classList.add('selected');
      }
      if (cellVal === this.focused) {
        classList.add('focused');
      }
    }

    changeFocusedCell(cellIndex) {
      this.grid.querySelectorAll('.focused').forEach((el) => {
        el.classList.remove('focused');
      });
      this.grid.children[cellIndex].classList.add('focused');
    }
  }

  class DaysView extends View {
    constructor(picker) {
      super(picker, {
        id: 0,
        name: 'days',
        cellClass: 'day',
      });
    }

    init(options, onConstruction = true) {
      if (onConstruction) {
        const inner = parseHTML(daysTemplate).firstChild;
        this.dow = inner.firstChild;
        this.grid = inner.lastChild;
        this.element.appendChild(inner);
      }
      super.init(options);
    }

    setOptions(options) {
      let updateDOW;

      if ('minDate' in options) {
        this.minDate = options.minDate;
      }
      if ('maxDate' in options) {
        this.maxDate = options.maxDate;
      }
      if (options.checkDisabled) {
        this.checkDisabled = options.checkDisabled;
      }
      if (options.daysOfWeekDisabled) {
        this.daysOfWeekDisabled = options.daysOfWeekDisabled;
        updateDOW = true;
      }
      if (options.daysOfWeekHighlighted) {
        this.daysOfWeekHighlighted = options.daysOfWeekHighlighted;
      }
      if ('todayHighlight' in options) {
        this.todayHighlight = options.todayHighlight;
      }
      if ('weekStart' in options) {
        this.weekStart = options.weekStart;
        this.weekEnd = options.weekEnd;
        updateDOW = true;
      }
      if (options.locale) {
        const locale = this.locale = options.locale;
        this.dayNames = locale.daysMin;
        this.switchLabelFormat = locale.titleFormat;
        updateDOW = true;
      }
      if ('beforeShowDay' in options) {
        this.beforeShow = typeof options.beforeShowDay === 'function'
          ? options.beforeShowDay
          : undefined;
      }

      if ('weekNumbers' in options) {
        if (options.weekNumbers && !this.weekNumbers) {
          const weeksElem = parseHTML(weekNumbersTemplate).firstChild;
          this.weekNumbers = {
            element: weeksElem,
            dow: weeksElem.firstChild,
            weeks: weeksElem.lastChild,
          };
          this.element.insertBefore(weeksElem, this.element.firstChild);
        } else if (this.weekNumbers && !options.weekNumbers) {
          this.element.removeChild(this.weekNumbers.element);
          this.weekNumbers = null;
        }
      }

      if ('getWeekNumber' in options) {
        this.getWeekNumber = options.getWeekNumber;
      }

      if ('showDaysOfWeek' in options) {
        if (options.showDaysOfWeek) {
          showElement(this.dow);
          if (this.weekNumbers) {
            showElement(this.weekNumbers.dow);
          }
        } else {
          hideElement(this.dow);
          if (this.weekNumbers) {
            hideElement(this.weekNumbers.dow);
          }
        }
      }

      // update days-of-week when locale, daysOfweekDisabled or weekStart is changed
      if (updateDOW) {
        Array.from(this.dow.children).forEach((el, index) => {
          const dow = (this.weekStart + index) % 7;
          el.textContent = this.dayNames[dow];
          el.className = this.daysOfWeekDisabled.includes(dow) ? 'dow disabled' : 'dow';
        });
      }
    }

    // Apply update on the focused date to view's settings
    updateFocus() {
      const viewDate = new Date(this.picker.viewDate);
      const viewYear = viewDate.getFullYear();
      const viewMonth = viewDate.getMonth();
      const firstOfMonth = dateValue(viewYear, viewMonth, 1);
      const start = dayOfTheWeekOf(firstOfMonth, this.weekStart, this.weekStart);

      this.first = firstOfMonth;
      this.last = dateValue(viewYear, viewMonth + 1, 0);
      this.start = start;
      this.focused = this.picker.viewDate;
    }

    // Apply update on the selected dates to view's settings
    updateSelection() {
      const {dates, rangepicker} = this.picker.datepicker;
      this.selected = dates;
      if (rangepicker) {
        this.range = rangepicker.dates;
      }
    }

     // Update the entire view UI
    render() {
      // update today marker on ever render
      this.today = this.todayHighlight ? today() : undefined;

      this.prepareForRender(
        formatDate(this.focused, this.switchLabelFormat, this.locale),
        this.first <= this.minDate,
        this.last >= this.maxDate
      );

      if (this.weekNumbers) {
        const weekStart = this.weekStart;
        const startOfWeek = dayOfTheWeekOf(this.first, weekStart, weekStart);
        Array.from(this.weekNumbers.weeks.children).forEach((el, index) => {
          const dateOfWeekStart = addWeeks(startOfWeek, index);
          el.textContent = this.getWeekNumber(dateOfWeekStart, weekStart);
          if (index > 3) {
            el.classList[dateOfWeekStart > this.last ? 'add' : 'remove']('next');
          }
        });
      }
      Array.from(this.grid.children).forEach((el, index) => {
        const current = addDays(this.start, index);
        const dateObj = new Date(current);
        const day = dateObj.getDay();
        const extraClasses = [];

        if (this.today === current) {
          extraClasses.push('today');
        }
        if (this.daysOfWeekHighlighted.includes(day)) {
          extraClasses.push('highlighted');
        }

        this.renderCell(
          el,
          dateObj.getDate(),
          current,
          current,
          this,
          current < this.minDate
            || current > this.maxDate
            || this.daysOfWeekDisabled.includes(day),
          extraClasses
        );
      });
    }

    // Update the view UI by applying the changes of selected and focused items
    refresh() {
      const range = this.range || [];
      Array.from(this.grid.children).forEach((el) => {
        this.refreshCell(el, Number(el.dataset.date), this.selected, range);
      });
    }

    // Update the view UI by applying the change of focused item
    refreshFocus() {
      this.changeFocusedCell(Math.round((this.focused - this.start) / 86400000));
    }
  }

  function computeMonthRange(range, thisYear) {
    if (!range || !range[0] || !range[1]) {
      return;
    }

    const [[startY, startM], [endY, endM]] = range;
    if (startY > thisYear || endY < thisYear) {
      return;
    }
    return [
      startY === thisYear ? startM : -1,
      endY === thisYear ? endM : 12,
    ];
  }

  class MonthsView extends View {
    constructor(picker) {
      super(picker, {
        id: 1,
        name: 'months',
        cellClass: 'month',
      });
    }

    init(options, onConstruction = true) {
      if (onConstruction) {
        this.grid = this.element;
        this.element.classList.add('months', 'datepicker-grid');
        this.grid.appendChild(parseHTML(createTagRepeat('span', 12, {'data-month': ix => ix})));
        this.first = 0;
        this.last = 11;
      }
      super.init(options);
    }

    setOptions(options) {
      if (options.locale) {
        this.monthNames = options.locale.monthsShort;
      }
      if ('minDate' in options) {
        if (options.minDate === undefined) {
          this.minYear = this.minMonth = this.minDate = undefined;
        } else {
          const minDateObj = new Date(options.minDate);
          this.minYear = minDateObj.getFullYear();
          this.minMonth = minDateObj.getMonth();
          this.minDate = minDateObj.setDate(1);
        }
      }
      if ('maxDate' in options) {
        if (options.maxDate === undefined) {
          this.maxYear = this.maxMonth = this.maxDate = undefined;
        } else {
          const maxDateObj = new Date(options.maxDate);
          this.maxYear = maxDateObj.getFullYear();
          this.maxMonth = maxDateObj.getMonth();
          this.maxDate = dateValue(this.maxYear, this.maxMonth + 1, 0);
        }
      }
      if (options.checkDisabled) {
        this.checkDisabled = this.isMinView || options.datesDisabled === null
          ? options.checkDisabled
          : () => false;
      }
      if ('beforeShowMonth' in options) {
        this.beforeShow = typeof options.beforeShowMonth === 'function'
          ? options.beforeShowMonth
          : undefined;
      }
    }

    // Update view's settings to reflect the viewDate set on the picker
    updateFocus() {
      const viewDate = new Date(this.picker.viewDate);
      this.year = viewDate.getFullYear();
      this.focused = viewDate.getMonth();
    }

    // Update view's settings to reflect the selected dates
    updateSelection() {
      const {dates, rangepicker} = this.picker.datepicker;
      this.selected = dates.reduce((selected, timeValue) => {
        const date = new Date(timeValue);
        const year = date.getFullYear();
        const month = date.getMonth();
        if (selected[year] === undefined) {
          selected[year] = [month];
        } else {
          pushUnique(selected[year], month);
        }
        return selected;
      }, {});
      if (rangepicker && rangepicker.dates) {
        this.range = rangepicker.dates.map(timeValue => {
          const date = new Date(timeValue);
          return isNaN(date) ? undefined : [date.getFullYear(), date.getMonth()];
        });
      }
    }

    // Update the entire view UI
    render() {
      this.prepareForRender(
        this.year,
        this.year <= this.minYear,
        this.year >= this.maxYear
      );

      const selected = this.selected[this.year] || [];
      const yrOutOfRange = this.year < this.minYear || this.year > this.maxYear;
      const isMinYear = this.year === this.minYear;
      const isMaxYear = this.year === this.maxYear;
      const range = computeMonthRange(this.range, this.year);

      Array.from(this.grid.children).forEach((el, index) => {
        const date = regularizeDate(new Date(this.year, index, 1), 1, this.isRangeEnd);

        this.renderCell(
          el,
          this.monthNames[index],
          index,
          date,
          {selected, range},
          yrOutOfRange
            || isMinYear && index < this.minMonth
            || isMaxYear && index > this.maxMonth
        );
      });
    }

    // Update the view UI by applying the changes of selected and focused items
    refresh() {
      const selected = this.selected[this.year] || [];
      const range = computeMonthRange(this.range, this.year) || [];
      Array.from(this.grid.children).forEach((el, index) => {
        this.refreshCell(el, index, selected, range);
      });
    }

    // Update the view UI by applying the change of focused item
    refreshFocus() {
      this.changeFocusedCell(this.focused);
    }
  }

  function toTitleCase(word) {
    return [...word].reduce((str, ch, ix) => str += ix ? ch : ch.toUpperCase(), '');
  }

  // Class representing the years and decades view elements
  class YearsView extends View {
    constructor(picker, config) {
      super(picker, config);
    }

    init(options, onConstruction = true) {
      if (onConstruction) {
        this.navStep = this.step * 10;
        this.beforeShowOption = `beforeShow${toTitleCase(this.cellClass)}`;
        this.grid = this.element;
        this.element.classList.add(this.name, 'datepicker-grid');
        this.grid.appendChild(parseHTML(createTagRepeat('span', 12)));
      }
      super.init(options);
    }

    setOptions(options) {
      if ('minDate' in options) {
        if (options.minDate === undefined) {
          this.minYear = this.minDate = undefined;
        } else {
          this.minYear = startOfYearPeriod(options.minDate, this.step);
          this.minDate = dateValue(this.minYear, 0, 1);
        }
      }
      if ('maxDate' in options) {
        if (options.maxDate === undefined) {
          this.maxYear = this.maxDate = undefined;
        } else {
          this.maxYear = startOfYearPeriod(options.maxDate, this.step);
          this.maxDate = dateValue(this.maxYear, 11, 31);
        }
      }
      if (options.checkDisabled) {
        this.checkDisabled = this.isMinView || options.datesDisabled === null
          ? options.checkDisabled
          : () => false;
      }
      if (this.beforeShowOption in options) {
        const beforeShow = options[this.beforeShowOption];
        this.beforeShow = typeof beforeShow === 'function' ? beforeShow : undefined;
      }
    }

    // Update view's settings to reflect the viewDate set on the picker
    updateFocus() {
      const viewDate = new Date(this.picker.viewDate);
      const first = startOfYearPeriod(viewDate, this.navStep);
      const last = first + 9 * this.step;

      this.first = first;
      this.last = last;
      this.start = first - this.step;
      this.focused = startOfYearPeriod(viewDate, this.step);
    }

    // Update view's settings to reflect the selected dates
    updateSelection() {
      const {dates, rangepicker} = this.picker.datepicker;
      this.selected = dates.reduce((years, timeValue) => {
        return pushUnique(years, startOfYearPeriod(timeValue, this.step));
      }, []);
      if (rangepicker && rangepicker.dates) {
        this.range = rangepicker.dates.map(timeValue => {
          if (timeValue !== undefined) {
            return startOfYearPeriod(timeValue, this.step);
          }
        });
      }
    }

    // Update the entire view UI
    render() {
      this.prepareForRender(
        `${this.first}-${this.last}`,
        this.first <= this.minYear,
        this.last >= this.maxYear
      );

      Array.from(this.grid.children).forEach((el, index) => {
        const current = this.start + (index * this.step);
        const date = regularizeDate(new Date(current, 0, 1), 2, this.isRangeEnd);

        el.dataset.year = current;
        this.renderCell(
          el,
          current,
          current,
          date,
          this,
          current < this.minYear || current > this.maxYear
        );
      });
    }

    // Update the view UI by applying the changes of selected and focused items
    refresh() {
      const range = this.range || [];
      Array.from(this.grid.children).forEach((el) => {
        this.refreshCell(el, Number(el.textContent), this.selected, range);
      });
    }

    // Update the view UI by applying the change of focused item
    refreshFocus() {
      this.changeFocusedCell(Math.round((this.focused - this.start) / this.step));
    }
  }

  function triggerDatepickerEvent(datepicker, type) {
    const detail = {
      date: datepicker.getDate(),
      viewDate: new Date(datepicker.picker.viewDate),
      viewId: datepicker.picker.currentView.id,
      datepicker,
    };
    datepicker.element.dispatchEvent(new CustomEvent(type, {detail}));
  }

  // direction: -1 (to previous), 1 (to next)
  function goToPrevOrNext(datepicker, direction) {
    const {config, picker} = datepicker;
    const {currentView, viewDate} = picker;
    let newViewDate;
    switch (currentView.id) {
      case 0:
        newViewDate = addMonths(viewDate, direction);
        break;
      case 1:
        newViewDate = addYears(viewDate, direction);
        break;
      default:
        newViewDate = addYears(viewDate, direction * currentView