Date Append Offset

Ensure all ISO date strings include the correct timezone offset — safely, without shifting time.

Date Append Offset is a lightweight TypeScript utility that ensures any ISO date string has a proper timezone offset, without modifying the original time or date.

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✅ Features

• 🕒 Preserves the original time and date
• 🌐 Appends the correct offset using IANA timezones (e.g. "America/Sao_Paulo")
• ✨ Supports partial inputs like:
  • 2025-06-12
  • 2025-06-12T12:00
  • 2025-06-12T12:00:00
• 🔧 Normalizes:
  • Missing seconds
  • Milliseconds
• 🛡️ Validates inputs and avoids invalid cases like Z-03:00

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📦 Installation

npm install date-append-offset

## 📦 Usage

```js
import { appendOffset } from 'date-append-offset';

// Adds offset and completes missing time
appendOffset('2025-06-12', 'America/Sao_Paulo');
// → '2025-06-12T00:00:00-03:00'

// Adds offset and seconds
appendOffset('2025-06-12T12:00', 'America/Manaus');
// → '2025-06-12T12:00:00-04:00'

// Keeps milliseconds and converts Z to +00:00
appendOffset('2025-06-12T12:00:00.123Z', 'America/Sao_Paulo');
// → '2025-06-12T12:00:00.123+00:00'

// Already has an offset: returns as-is
appendOffset('2025-06-12T12:00:00-03:00', 'America/Manaus');
// → '2025-06-12T12:00:00-03:00'

// Invalid timezone + malformed input throws
appendOffset('2025-06-12T12:00Z-03:00', 'America/Sao_Paulo');
// → ❌ Error: Invalid date: cannot mix Z (UTC) with offset