Set the time of a date to midnight
Return the start of the UTC day of a date-time.
function midnightUtc(now) { const d = new Date(now); d.setUTCHours(0, 0, 0, 0); return d.toISOString(); }Input & expected output
Input
"2026-10-28T14:05:00Z"Expected output
"2026-10-28T00:00:00.000Z"The edge case
Input
"2026-10-28T23:30:00-03:00"Expected output
"2026-10-29T00:00:00.000Z"Know the limits
- The original used local midnight via setHours; this version is UTC so it is the same on every server. Use setHours for the reader’s local day.
The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.
Source & maintenance
Based on Initialize the current date but set time to midnight from the original 1loc collection by Nguyen Huu Phuoc. Copyright (c) 2020 phuoc-ng. MIT licensed.
Takes the time as an input and returns UTC midnight; the original used local midnight. Original MDX retained as inert source evidence.
Maintained by Oveyon. Source commit: 14b481cf60df. Read the license.
Keep exploring
- Compare two dates — Compare validated ISO calendar dates in UTC and return -1, 0 or 1.
- Add AM PM suffix to an hour — Turn an hour from 0 to 23 into a 12-hour label with am or pm.
- Calculate the number of days between two dates — Count whole calendar days between two YYYY-MM-DD dates.