timezone-mock

library1.4.2jsnpmunverified

A JavaScript library to mock the local timezone for testing purposes. Version 1.4.2 is current stable, with infrequent releases. It replaces the global Date constructor with a mocked version that behaves as if in a specified timezone, including DST transitions. Key differentiators: lightweight, no dependencies, supports multiple timezones (US/Pacific, US/Eastern, Brazil/East, UTC, Europe/London, Australia/Adelaide) and GMT offsets, and includes TypeScript types. Unlike full timezone libraries, it focuses solely on mocking for testing, not on timezone conversions or comprehensive data.

testing

npm install timezone-mock

github ↗package ↗

INSTALL

IMPORT

SIG · TIMEZONE-MOCK

timezone-mock

testingjavascriptv1.4.2

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

✓ import { register } from 'timezone-mock'

✗ import timezoneMock from 'timezone-mock'; timezoneMock.register()

Package exports named exports; default import works but is not typical.

unregister

✓ import { unregister } from 'timezone-mock'

✗ const { unregister } = require('timezone-mock'); // CommonJS works but ESM preferred

_Date

✓ import { _Date } from 'timezone-mock'

Only available after register() is called; gives access to original Date.

options

✓ import { options } from 'timezone-mock'

Accepts an object with fallbackFn for unparseable dates.

Demonstrates registering mock timezone, creating a Date, and unregistering. Also shows DST transition test.

import { register, unregister } from 'timezone-mock'; register('US/Pacific'); const date = new Date('2023-06-15T12:00:00'); console.log(date.getHours()); // Output may differ from local timezone unregister(); // Test DST behavior register('US/Eastern'); const dstDate = new Date('2023-03-12T02:30:00'); // DST transition console.log(dstDate.getHours()); // 3 (spring ahead) unregister();

Debug

Known issues

gotchatimezone-mock replaces the global Date constructor; if used in a test suite, must call unregister() after each test to avoid cross-test contamination.

fix

Use afterEach or cleanup hooks to call unregister().

affects: >=0.0.0

breakingNode v8.0.0 changed ISO string 'YYYY-MM-DDTHH:MM:SS' from UTC to local interpretation. timezone-mock treats it as local, matching Node v8+; tests on older Node may behave differently.

fix

Ensure Node >= 8 for consistent behavior, or avoid date string parsing in tests.

affects: >=1.0.0

deprecatedBrazil/East timezone no longer observes DST as of 2019; DST transition only applies to dates 2018 and earlier. Using it for modern dates may not test DST correctly.

fix

Use US/Pacific or US/Eastern for DST testing.

affects: >=1.4.0

gotchaTimezones Etc/GMT+X have inverted sign: Etc/GMT+5 is UTC-5, not UTC+5. Common mistake.

fix

Remember Etc/GMT+N = UTC-N, not UTC+N.

affects: >=1.4.0

gotchaThe _Date property is only available after register() is called; accessing it before results in undefined.

fix

Call register() first, then access timezone_mock._Date.

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: timezone_mock.register is not a function

Importing default instead of named export (e.g., import timezoneMock from 'timezone-mock' then timezoneMock.register).

fix

Use import { register } from 'timezone-mock' OR import * as timezoneMock from 'timezone-mock' then timezoneMock.register.

AssertionError [ERR_ASSERTION]: Expected values to be strictly equal. Expected: 1609459200000. Received: 1609455600000

Date comparison fails because mock timezone changes the timestamp for date string '2021-01-01T00:00:00' (interpreted as local time).

fix

Use UTC dates (new Date('2021-01-01T00:00:00Z')) or ensure consistent timezone handling.

Upgrade

Version history

1.4.2latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

6 hits · last 30 days

node

Resources

githubhttps://github.com/Jimbly/timezone-mock ↗

packagehttps://www.npmjs.com/package/timezone-mock ↗