How to fix Error: Invalid timezone string (TZ environment variable malformed) in Node.js

# On Linux/macOS
echo $TZ

# Check in Node.js
node -e "console.log(process.env.TZ)"

# Inside a running Node.js app
console.log('TZ:', process.env.TZ);

# Correct IANA timezone formats
TZ='America/New_York' node app.js
TZ='Europe/London' node app.js
TZ='Asia/Tokyo' node app.js
TZ='Australia/Sydney' node app.js
TZ='UTC' node app.js
TZ='Etc/UTC' node app.js

# Case-sensitive - exact capitalization matters
# America/new_york is WRONG
# america/new_york is WRONG
# America/New_York is CORRECT

// Set at application start, before importing other modules
process.env.TZ = 'America/New_York';

// Then import and use date functions
const app = require('./app');

// Verify it's applied
const now = new Date();
console.log('Current time in', process.env.TZ, ':', now.toString());
console.log('Timezone offset:', now.getTimezoneOffset());

// First thing in your app
require('dotenv').config();

process.env.TZ = process.env.TZ || 'UTC';

// Then continue with rest of app
const express = require('express');

# Dockerfile
FROM node:20-alpine

# Set valid timezone
ENV TZ=America/New_York

WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "app.js"]

version: '3'
services:
  app:
    build: .
    environment:
      - TZ=America/New_York  # Valid IANA timezone

# WRONG - this causes the error
export TZ=/etc/localtime
node app.js

# WRONG - this also fails
export TZ=/usr/share/zoneinfo/America/New_York
node app.js

# CORRECT - use the timezone identifier directly
export TZ=America/New_York
node app.js

# This might work on Linux (but not all systems)
TZ=:/etc/localtime node app.js

// List of commonly used valid timezones
const VALID_TIMEZONES = [
  'UTC',
  'America/New_York',
  'America/Chicago',
  'America/Denver',
  'America/Los_Angeles',
  'Europe/London',
  'Europe/Paris',
  'Europe/Berlin',
  'Asia/Tokyo',
  'Asia/Shanghai',
  'Australia/Sydney',
];

function validateTimezone(tz) {
  if (!tz) return 'UTC'; // Default fallback

  // Simple check - a real implementation should validate against the full IANA database
  if (VALID_TIMEZONES.includes(tz)) {
    return tz;
  }

  console.warn(`Invalid timezone "${tz}", using UTC instead`);
  return 'UTC';
}

// At startup
const validTZ = validateTimezone(process.env.TZ);
process.env.TZ = validTZ;

console.log(`Timezone set to: ${validTZ}`);

// Using moment-timezone (if available in your project)
const moment = require('moment-timezone');

const tz = process.env.TZ;
if (!moment.tz.zone(tz)) {
  console.error(`Invalid timezone: ${tz}`);
  process.env.TZ = 'UTC';
}

// test/timezone.test.js
describe('Timezone handling', () => {
  test('TZ environment variable is valid', () => {
    const tz = process.env.TZ;
    expect(tz).toBeDefined();

    // Attempt to use a date with the TZ
    const now = new Date();
    const formatted = now.toLocaleString('en-US', {
      timeZone: tz
    });

    // If this doesn't throw, timezone is valid
    expect(formatted).toBeTruthy();
  });

  test('dates display correct timezone', () => {
    process.env.TZ = 'America/New_York';

    const now = new Date('2024-01-15T12:00:00Z');
    const estTime = now.toLocaleString('en-US', {
      timeZone: 'America/New_York'
    });

    // EST is UTC-5 in January
    expect(estTime).toContain('7:00:00 AM');
  });
});

# .github/workflows/test.yml
jobs:
  test:
    runs-on: ubuntu-latest
    env:
      TZ: America/New_York
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-node@v3
        with:
          node-version: '20'
      - run: npm test