Get the timezone string

Read the runtime’s IANA time zone, such as America/Sao_Paulo.

JavaScriptNode.js & browsers Version 1.0.0 · MIT · .md

function getTimezone() { return Intl.DateTimeFormat().resolvedOptions().timeZone; }

Usage

getTimezone(); // e.g. 'America/Sao_Paulo'
const at = new Date('2026-10-28T12:00:00Z');
at.toLocaleTimeString('en-GB', { timeZone: 'America/Sao_Paulo', hour: '2-digit', minute: '2-digit' }); // → '09:00'
at.toLocaleTimeString('en-GB', { timeZone: getTimezone(), hour: '2-digit', minute: '2-digit' }); // e.g. '09:00'

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

Know the limits

• Returns the zone of the runtime: the visitor’s in a browser, the server’s (often UTC) in Node.js. Store instants in UTC and convert for display.
• A zone is not an offset: America/Sao_Paulo has had no daylight saving time since 2019, while other zones still shift twice a year.

The function above is the code the usage lines run. It does not validate its arguments; add checks where it receives untrusted input.

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.