Writing

Luxon datetime library defaults startOf and endOf methods to UTC. But this isn’t great for end users who don’t live in UTC / GMT. To offset this, we need to grab the time zone offset from the user’s system.

const systemTimeZoneOffsetInMinutes = new Date().getTimezoneOffset();  
const systemTimeZoneOffsetInHours = systemTimeZoneOffset / 60;

Then we can add the offset to the Luxon datetime object.

const now = DateTime.now();
const startOfLocalDay = now.startOf('day').plus({ hours: systemTimeZoneOffsetInHours });
const endOfLocalDay = now.endOf('day').plus({ hours: systemTimeZoneOffsetInHours });