startOfWeek
Get the first boundary of the week (Monday)
Returns the first boundary of the ISO week (Monday). PlainDate inputs stay in calendar space and return a PlainDate; providing a timezone returns a ZonedDateTime at the start of Monday.
Signature
function startOfWeek(
input: Temporal.Instant | Temporal.ZonedDateTime
): Temporal.ZonedDateTime
function startOfWeek(input: Temporal.PlainDate): Temporal.PlainDate
function startOfWeek(
input: Temporal.PlainDate,
timezone: Timezone
): Temporal.ZonedDateTimeParameters
| Parameter | Type | Description |
|---|---|---|
input | Temporal.Instant | Temporal.ZonedDateTime | Temporal.PlainDate | The date or datetime to get the start of week for |
timezone | Timezone | Required only when converting a PlainDate boundary to a ZonedDateTime |
Returns
A Temporal.PlainDate for calendar-only input, or a Temporal.ZonedDateTime at the start of Monday for datetime input or an explicit timezone.
Examples
From Instant (Monday)
import { startOfWeek } from '@gobrand/tiempo';
const instant = Temporal.Instant.from('2025-01-20T12:00:00Z'); // Monday
startOfWeek(instant);
// 2025-01-20T00:00:00Z[UTC] (same day, already Monday)From ZonedDateTime (Wednesday)
const zoned = Temporal.ZonedDateTime.from('2025-01-22T15:30:00-05:00[America/New_York]');
startOfWeek(zoned);
// 2025-01-20T00:00:00-05:00[America/New_York] (previous Monday)From PlainDate
const date = Temporal.PlainDate.from('2025-01-22');
startOfWeek(date);
// 2025-01-20
startOfWeek(date, 'America/New_York');
// 2025-01-20T00:00:00-05:00[America/New_York]Common Patterns
This week's range
import { startOfWeek, endOfWeek } from '@gobrand/tiempo';
const now = Temporal.Now.zonedDateTimeISO('America/New_York');
const weekStart = startOfWeek(now);
const weekEnd = endOfWeek(now);