Docs: improve sample code for global catch all exceptions

I’m submitting a…

[ ] Regression 
[ ] Bug report
[ ] Feature request
[x] Documentation issue or request (new chapter/page)
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

Exceptions chapter, possible example code improvement.

Expected behavior

If you were to implement the “Catch Everything” code sample in the Exception filters chapter, it would work as described.

Minimal reproduction of the problem with instructions

Simply implement this http-exception filter (with empty @Catch() decorator) to handle all exceptions as shown in the docs. Then issue a throw new Error('boom'); in the CatsController to simulate a non-HTTP exception arising, and make the http request.

What is the motivation / use case for changing the behavior?

The problem is that the code sample includes the code: const status = exception.getStatus(); but a vanilla Error class doesn’t have this method.

I would propose something like the following. If acceptable, I’ll include it in an upcoming PR for this chapter.

import {
  ExceptionFilter,
  Catch,
  ArgumentsHost,
  HttpException,
} from '@nestjs/common';
import { Request, Response } from 'express';

@Catch()
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const request = ctx.getRequest<Request>();

    // default HTTP response code for non HttpException errors is
    // 500 - Internal Server Error
    let status = 500;
    if (exception instanceof HttpException) {
      status = exception.getStatus();
    }

    response.status(status).json({
      statusCode: status,
      timestamp: new Date().toISOString(),
      path: request.url,
    });
  }
}

Environment

For Tooling issues:
- Node version: XX  
- Platform:  

Others:

[kamilmysliwiec]

Good point @lazarljubenovic. Also, we could define 500 value as a constant variable (or use HttpStatus enum) instead of adding a comment.

const status = exception instanceof HttpException
  ? exception.getStatus()
  : HttpStatus.INTERNAL_SERVER_EROR;

It’s ^ self-descriptive I think.

[lazarljubenovic]

It might be clearer to write

const status = exception instanceof HttpException
  ? exception.getStatus()
  : 500

instead of overwriting status, since it’s only a single condition.