> For the complete documentation index, see [llms.txt](https://dsheiko.gitbook.io/bycontract/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dsheiko.gitbook.io/bycontract/validation-exceptions.md).

# Validation Exceptions

```javascript
import { validate, Exception } from "bycontract";
try {
  validate( 1, "NaN" );
} catch( err ) {
  console.log( err instanceof Error ); // true
  console.log( err instanceof TypeError ); // true
  console.log( err instanceof Exception ); // true
  console.log( err.name ); // ByContractError
  console.log( err.message ); // expected nan but got number
}
```