Avoid `Record<string, unknown>` after testing existence of variable object key?

[dark zodiac]

Is there a way to avoid the as Record<string, unknown> in this case?

Here is the code:

export const requiredValidator = <Y>(
  input: object,
  fieldName: string,
  innerValidator: (_input: unknown) => E.Either<InputValidationError, Y>,
) => {
  if (fieldName in input) {
    return innerValidator((input as Record<string, unknown>)[fieldName]);
  }
  return E.left(inputValidationError(`'${fieldName}' ${Constants.VALIDATION_ERROR_MESSAGES.NOT_VALID}`));
};

as Record<string, unknown> feels.... dirty.

[fast nova]

why not input: Partial<Record<string, unknown>>?

[dark zodiac]

Oh, interesting. And I don't even need to prove to the TS type checker that input is a Partial<Record<string, unknown>>, as long as it is an object. That's perfect.

Thanks!

[dark zodiac]

But then why doesn't the TS checker directly allow input[fieldName] when input is only known as an object?

[fast nova]

object doesn't imply there are any keys

whereas Record<string, unknown> does

[dark zodiac]

In that case, can assigning an object to a Partial<Record<string, unknown>> ever cause type-related problems that are not caught by the TS checker?

[fast nova]

yes, if you mutate it

not sure if adding a Readonly<> will fix that

[fast nova]

for reading, its perfectly safe of course

objects can all be indexed by any string, at runtime

it's just that some keys will be undefined - which is what the Partial is for

I'm not quite sure its needed here actually, since unknown includes undefined

but i still do think it makes the meaning of the type clearer, if nothing else

[dark zodiac]

I see.

[dark zodiac]

Thanks for the extra explanation.