# assertDateBefore

Source: https://smartassertions.dev/assertions/assertDateBefore/
Index of every page: https://smartassertions.dev/llms.txt

Assert that a Date holds an earlier instant than the expected one, with type-narrowing.

Comparing two instants through assertLessThan means reading epoch milliseconds out of the failure.

This reports both Dates in ISO form.

## Usage

```ts
import { assertDateBefore } from "@kensio/smartass";

const createdAt: unknown = new Date("2026-01-01T00:00:00.000Z");

assertDateBefore(createdAt, new Date("2026-06-01T00:00:00.000Z"));

// createdAt is now narrowed to Date
```

## Source

Source file: [`src/assert/date-before/date-before.assert.ts`](https://github.com/KensioSoftware/smartass/blob/main/src/assert/date-before/date-before.assert.ts)