Date/Since
1.38.0startOfDay
Returns a new Date set to the first millisecond of the given day.
startOfDay(date):DateParameters
dateDaterequiredThe date whose start of day should be returned.
Returns
DateA new Date set to 00:00:00.000 of the given day.
Examples
01
Basic usage
Get the start of a specific day.
TypeScript
import { startOfDay } from "@cyref/js";
const date = new Date("2026-01-15T10:30:00");
const result = startOfDay(date);
console.log(result);
// 2026-01-15T00:00:00.00002
Date without time
The function sets the time to the first millisecond of that day.
TypeScript
import { startOfDay } from "@cyref/js";
const date = new Date("2026-03-20");
const result = startOfDay(date);
console.log(result);
// 2026-03-20T00:00:00.00003
Original date remains unchanged
startOfDay creates a new Date object, so the original date is not modified.
TypeScript
import { startOfDay } from "@cyref/js";
const date = new Date("2026-05-10T14:30:00");
const result = startOfDay(date);
console.log(date);
// 2026-05-10T14:30:00
console.log(result);
// 2026-05-10T00:00:00.00004
Time components are reset
Hours, minutes, seconds, and milliseconds are all reset to zero.
TypeScript
import { startOfDay } from "@cyref/js";
const date = new Date("2026-08-25T18:45:32.500");
const result = startOfDay(date);
console.log(result.getHours());
// 0
console.log(result.getMinutes());
// 0
console.log(result.getSeconds());
// 0
console.log(result.getMilliseconds());
// 005
Date already at the start of the day
If the date is already at the start of the day, the returned Date has the same date and time value.
TypeScript
import { startOfDay } from "@cyref/js";
const date = new Date("2026-09-10T00:00:00.000");
const result = startOfDay(date);
console.log(result);
// 2026-09-10T00:00:00.000Built with@cyref/js·Official documentation