More user friendly ErrorObject TypeScript type

[torifat]

What problem do you want to solve?
In its current state ErrorObject is not very user friendly in certain scenarios. For example:

function useError(ajvError: ErrorObject) {
  switch(ajvError.keyword) {
    case 'enum': {
      // ErrorParameters
      ajvError.params
    }
  }
}

It would be really useful if we could get EnumParams here, instead of ErrorParameters. It's possible to use type-guards to achieve something similar but the code gets a bit messier.

What do you think is the correct solution to problem?
IMO it can be improved by using discriminated unions. If we do something like:

interface IErrorObject<T, U> {
  keyword: T,
  params: U,
  ...
}

type EnumErrorObject = IErrorObject<'enum', EnumParams>;
type RequiredErrorObject = IErrorObject<'required', RequiredParams>;
...

export type ErrorObject = EnumErrorObject | RequiredErrorObject | ...;

Then we will get EnumParams inside the enum case.

function useError(ajvError: ErrorObject) {
  switch(ajvError.keyword) {
    case 'enum': {
      // EnumParams
      ajvError.params
    }
  }
}

Will you be able to implement it?
Yes

[torifat]

@epoberezkin any thoughts?

[epoberezkin]

@torifat Sorry for ignoring it... Looking at it now - it is probably the right approach.

Now that it is re-written in typescript - probably error type should be defined by each keyword locally (although given that it is returned via generated code it won't be connected to the actual code, just visually)

[epoberezkin]

The only problem I see with this approach is that ErrorObject should be an open union, to allow users extending it when they define custom keywords without modifying Ajv code base - trying to figure out how to do it in typescript... @torifat any suggestion would be fantastic.

[epoberezkin]

in v7-alpha