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Version: Next 🚧

Date utilities

The helpers the pickers use internally, exported for your own code. All of them:

  • work in local time (no UTC surprises)
  • never mutate their inputs
  • fall back to English names if Intl is missing or a locale is invalid
import { toDateKey, addDays, isSameDay, formatDate } from '@elik56a/react-native-pickers';

Arithmetic​

startOfDay​

startOfDay(d: Date): Date

Same day at 00:00:00.000.

startOfMonth​

startOfMonth(d: Date): Date

First day of the month at 00:00.

daysInMonth​

daysInMonth(year: number, month: number): number   // month is 0-based
daysInMonth(2028, 1) // 29

addDays​

addDays(d: Date, days: number): Date

Adds calendar days (negative to subtract), keeping hours and minutes (seconds and milliseconds are reset). DST-safe, because it works on date parts rather than milliseconds.

addMonths​

addMonths(d: Date, months: number): Date
addMonths(new Date(2026, 0, 31), 1) // Feb 28 2026 (clamped)

Clamps the day to the target month's length and keeps the time.

clampDate​

clampDate(d: Date, min?: Date | null, max?: Date | null): Date

Returns a copy of min / max when d is outside them (by exact time), else d.

Comparison​

isSameDay​

isSameDay(a?: Date | null, b?: Date | null): boolean

Same calendar day; false if either is null.

isSameMonth​

isSameMonth(a: Date, b: Date): boolean

compareDay​

compareDay(a: Date, b: Date): number   // < 0, 0, > 0

Compares calendar days, ignoring time. Use it as a sort comparator: dates.sort(compareDay).

isBetweenDays​

isBetweenDays(d: Date, start?: Date | null, end?: Date | null): boolean

true when d is strictly between start and end (exclusive), by day.

isOutOfRange​

isOutOfRange(d: Date, min?: Date | null, max?: Date | null): boolean

true when d's day is before min's day or after max's day.

Keys and grids​

toDateKey​

toDateKey(d: Date): string   // 'YYYY-MM-DD' in local time

The key format of markedDates. Use it instead of toISOString().slice(0, 10), which converts to UTC and can be off by a day.

buildMonthGrid​

buildMonthGrid(year: number, month: number, firstDayOfWeek = 0, fixedWeeks = true): Date[][]

Weeks Γ— 7 days for a month view, including leading and trailing days of neighbouring months. 6 weeks when fixedWeeks, else only as many as needed. Handy for custom calendars and heatmaps.

Locale​

getMonthNames​

getMonthNames(locale?: string, width: 'long' | 'short' = 'long'): string[]   // 12 names

getWeekdayNames​

getWeekdayNames(locale?: string, width: 'long' | 'short' | 'narrow' = 'short'): string[]

7 names indexed by JS day: 0 = Sunday.

formatMonthYear​

formatMonthYear(d: Date, locale?: string): string   // 'October 2026'

formatDate​

formatDate(d: Date, locale?: string, opts: Intl.DateTimeFormatOptions = { dateStyle: 'medium' }): string
formatDate(new Date(2026, 9, 14))                          // 'Oct 14, 2026'
formatDate(new Date(2026, 9, 14), 'de-DE', { dateStyle: 'full' }) // 'Mittwoch, 14. Oktober 2026'

Cached Intl.DateTimeFormat, falling back to YYYY-MM-DD.

uses12HourClock​

uses12HourClock(locale?: string): boolean

true when the locale formats hours with AM/PM.

getFirstDayOfWeek​

getFirstDayOfWeek(locale?: string): number   // 0 = Sunday … 6 = Saturday

From Intl.Locale week info when the runtime supports it; otherwise 0. Returns 0 when no locale is given.

getDayPeriods​

getDayPeriods(locale?: string): [string, string]   // ['AM', 'PM'], ['εˆε‰', '午後'], …