Expose schema validation errors

[dd-jonas]

Hi

I am using the built-in schema validation of this library, but in my use case I would like to have better access to the validation errors. I am using the onError hook to send those error to our error monitoring tool, but I noticed that this library throws a generic Error when schema validation fails.

My workaround looks like this

export const fetchJson = up(fetch, () => ({
  // other fields...

  onError: (error) => {
    if (isSchemaValidationError(error)) {
      Sentry.captureException(error, { level: 'error' });
    }
  },
}));

const isSchemaValidationError = (error: Error) => {
  try {
    const issues = JSON.parse(error.message);

    if (!Array.isArray(issues)) return false;

    return issues.every((issue) => 'message' in issue && 'path' in issue);
  } catch {
    return false;
  }
};

It would be nice to have a custom error built-in like the ResponseError, for example:

import { isSchemaValidationError } from 'up-fetch';

export const fetchJson = up(fetch, () => ({
  // other fields...

  onError: (error) => {
    if (isSchemaValidationError(error)) {
      Sentry.captureException(error, { level: 'error' });
      console.error(error.issues); // Would be nice if this was exposed as well
    }
  },
}));

What do you think? If this is out-of-scope of this library, I'm fine with my current workaround.

[L-Blondy]

Good idea, I opened the PR #19

Any feedback is welcome