Timezone Converter

The Timezone Converter bundles four modes behind a single tab bar: Time Converter, World Clock, Meeting Scheduler, and Unix Epoch. All time math is done with the browser's built-in Intl.DateTimeFormat API rather than a date library like moment or luxon, so the underlying IANA zone data ships with your browser. The tool exposes a curated list of 38 zones identified by their IANA names (America/New_York, Europe/London, Asia/Tokyo, Pacific/Auckland and so on) rather than raw fixed offsets, which matters because a named zone tracks daylight-saving changes across the year while a bare 'UTC-5' label does not. The list also includes a half-hour zone, Asia/Kolkata (India Standard Time, UTC+5:30), so conversions are not assumed to land on whole-hour boundaries.

World Clock mode ticks once per second via a setInterval timer and renders each added zone with its live time, its current short-offset string (pulled from Intl with timeZoneName: 'shortOffset', e.g. GMT+1), and a day/night indicator: a yellow Sun icon when the local hour is between 6 AM and 6 PM (hour >= 6 and < 18) and a blue Moon icon otherwise. Meeting Scheduler builds a 24-row grid, one row per hour 00:00 through 23:00, and color-codes every cell against your selected work-hours window (start and end hours are individually selectable across all 24 hours from 12 AM to 11 PM, defaulting to 9 AM-5 PM): a cell turns green only when every participant zone falls inside working hours, yellow when that particular zone is inside working hours but not all are, and dimmed otherwise, which makes overlapping availability across, by default, New York, London and Tokyo easy to spot.

Unix Epoch mode converts a timestamp in either seconds or milliseconds and renders six simultaneous outputs for the same instant: a UTC string (toUTCString), a local-time string (Date.toString), an ISO 8601 string (toISOString), a human relative phrase (e.g. '3 hours ago' or '2 days from now', computed from the difference against the current time and bucketed into just now / minutes / hours / days), and the raw seconds and milliseconds values, each individually copyable. A 'Set Current Time' button fills the field with now in the chosen unit. The mode tab, source/target zones, and epoch input/unit are persisted into the URL through a shareable-config mechanism so a specific conversion can be linked, while the World Clock zone list and the live clocks are kept local because they are time-sensitive. One honest caveat: the converter performs its zone shift by round-tripping a Date through toLocaleString offsets rather than a dedicated DST-aware library, so results on the exact day a region springs forward or falls back should be sanity-checked.