# Compare two dates

Compare validated ISO calendar dates in UTC and return -1, 0 or 1.

Canonical: https://1loc.dev/date-time/compare-two-dates/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function compareDates({ first, second }) { return Math.sign(new Date(first).getTime() - new Date(second).getTime()); }
```

## Input

```json
{
  "first": "2026-10-28",
  "second": "2026-10-29"
}
```

## Expected output

```json
-1
```

## Edge case

Input:
```json
{
  "first": "2024-02-29",
  "second": "2024-02-29"
}
```
Output:
```json
0
```

## Limits

- The lab requires real YYYY-MM-DD calendar dates and validates before execution.
- This compares UTC calendar dates, not local business days or ambiguous date strings.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/compare-two-dates.mdx
Source file (this edition): https://github.com/akamind/1loc/blob/0a77f131b22d2ba3b7ec1728846f900c22821678/contents/compare-two-dates.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Curated implementation; explicit input bounds, edge cases, local fixtures and rebuilt presentation. Original MDX retained as inert source evidence.