Return error message if isbn validation failed

[dwightkelly]

It would be useful to return an error message with details of why isbn validation failed.

[maxlath]

That could be nice, but would definitely be a breaking change, unless that behavior is activated by a flag.

[Roman991]

This could be an interesting feature.
Would u consider a PR with the following logic?

1. IF input length = 10 AND it != starts with 978|979 AND parse = null >> ERROR
2. ELSE IF input length = 13 AND it starts with 978|979 and parse = null >> ERROR
3. ELSE IF input length > 13 >> ERROR
4. ELSE >> null

so error is thrown only when there is formally ISBN-like input but after the parsing there is a null
883951856 (9 digits) >> null
97888 >> null
978883951856 >> null
9788839518569 >> valid
9788839518568 >> error

[maxlath]

Maybe such a feature could be a new function, such as parseStrict, or behind a flag: parse(isbn, { strict: true }). In both case, that would remove the problem of the breaking change.

Another idea: it could also (optionally?) enrich the error with the info gathered by the audit function