Date utils TypeScript helper for React

• getWeekStartsOn

  function

  The first day of the week for a locale, 0 (Sunday) to 6 like date-fns: 0 in en-US, 1 in en-GB and de-DE, 6 in ar-EG. From Intl week info where the browser has it, from a CLDR table where it does not (Firefox).

• getWeekendDays

  function

  The weekend days for a locale as weekday numbers: [6, 0] in en-US, [5, 6] in ar-EG. Calendars use it to tint weekends.

• getHourCycle

  function

  Whether a locale writes times on a 12 hour ("h12", en-US) or 24 hour clock ("h23", en-GB, de-DE).

• capitalize

  function

  Uppercases the first letter in the locale's rules, for month names that Intl writes in lowercase in some languages.

• getMonthNames

  function

  The twelve month names from Intl, January first and capitalized, in "long", "short" or "narrow" form. No bundled locale data.

• getWeekdayNames

  function

  Weekday names in display order from weekStartsOn, in "long", "short", "min" or "narrow" form. "min" is the two-letter calendar header (Su Mo Tu We Th Fr Sa).

• formatMonthYear

  function

  The calendar caption for a month: "September 2026" in en-US.

• getDateOrder

  function

  How a locale writes a numeric date: { order, separator, pattern }, e.g. MM/dd/yyyy in en-US and dd.MM.yyyy in de-DE.

• autoFormatDateInput

  function

  Inserts the locale's separators while someone types digits into a date field: "0923" becomes "09/23/" in en-US. Text with letters, like "tomorrow", passes through.

• formatDate

  function

  A date in the locale, numeric by default ("09/23/2026" in en-US) or with any Intl options ({ dateStyle: "medium" } gives "Sep 23, 2026"). "" for null or an invalid date.

• formatDateRange

  function

  A range through Intl formatRange, which writes the shared month and year only once. While only the start is picked it prints the start alone, followed by a dash.

• formatDayLabel

  function

  The long spoken form of a day for a day button's aria-label: "Wednesday, September 23, 2026".

• toISODate

  function

  "2026-09-23" in local time for hidden form inputs. Never uses toISOString, which converts to UTC and can land on the previous day.

• toISODateTime

  function

  "2026-09-23T14:30" in local time, for date and time inputs.

• fromISODate

  function

  Reads "2026-09-23" or "2026-09-23T14:30" back into a local Date; null when the text is not one.

• matchesDate

  function

  Whether a day matches a DateMatcher or a list of them. Calendars use it for disabled and marked days.

• isDateUnavailable

  function

  Whether a day falls outside min or max (by calendar day) or matches disabled. Takes (date, { min?, max?, disabled? }).

• getMonthWeeks

  function

  The weeks of a month grid, 7 days each from weekStartsOn, including the neighbor month's days that fill the first and last week. fixedWeeks always returns 6 weeks so the grid never changes height.

• normalizeRange

  function

  Puts from before to, swapping a range picked backwards. Nulls stay.

• isInRange

  function

  Whether a day is inside a range, both ends included.

• countDays

  function

  The days in a range, both ends included (a 3 night hotel stay is 4 days); 0 while the range is incomplete.

• getDatePresets

  function

  Single-day presets from a reference day: today, tomorrow, yesterday, nextWeek (same weekday) and nextMonth. Labels are the picker's job.

• getRangePresets

  function

  The usual report ranges from a reference day, ends included: last 7 days, this month, last quarter and more. "Last 7 days" ends today.

• parseTime

  function

  What someone typed as an "HH:mm" string, or null: "14:30", "1430", "14.30", "2:30 pm", "2p", "12am". Locale-free like <input type="time">.

• formatTime

  function

  An "HH:mm" value in the locale: "2:30 PM" in en-US, "14:30" in en-GB. hourCycle forces a 12 or 24 hour clock.

• getDayPeriodLabels

  function

  The locale's AM and PM labels, for a time picker's period toggle.

• timeToMinutes

  function

  "14:30" to 870 minutes after midnight; null when the value is not a time.

• minutesToTime

  function

  870 to "14:30", wrapping around midnight.

• setTime

  function

  A new Date on the same day at an "HH:mm" time.

• getTimeOfDay

  function

  The "HH:mm" time of a Date.

• DateRange

  type

  { from: Date | null; to: Date | null }, the value of range pickers.

• DateMatcher

  type

  What a calendar can disable or mark: a Date, a Date[], { from, to }, { before }, { after }, { dayOfWeek } or (date) => boolean.

• Weekday

  type

  0 (Sunday) to 6 (Saturday), like date-fns.

• ParseDateOptions

  type

  parseDate's options: locale, reference (the day "tomorrow" counts from) and keywords per language.

Files

• lib/date-utils.ts