Custom errors using TypeCompiler

[JimSalies]

First of all, thank you for this amazing lib!

I have been searching through documentation / PR and discussions and didn't find anything about using custom errors with typecompiler. Is it possible to use custom error messages? If so, how to do it?

[sinclairzx81]

@JimSalies Hi,

TypeBox doesn't handle automatic custom error messages internally, rather it requires implementers to remap the error objects yielded on .Errors() externally as they need them. This is usually handled by writing a mapping function over the top of .Errors() which implements any custom error mapping logic you need. The following code does a quick inline remap to demonstrate how you can extract and remap custom error messages applied to schemas.

const T = Type.Object({
  x: Type.Number({ errorMessage: 'X error' }),
  y: Type.Number({ errorMessage: 'Y error' }),
  z: Type.Number({ errorMessage: 'Z error' }),
})

const C = TypeCompiler.Compile(T)

// The failing schema is passed as a property on each `error` object. You can inspect 
// the schema and remap for any custom metadata found on it if necessary. Note, you 
// would typically wrap the following up in a function and use it in your applications
// validation pipeline.
const E = [...C.Errors({ x: '1', y: '2', z: '3' })].map(error => {
  return (typeof error.schema.errorMessage === 'string')
    ? {...error, message: error.schema.errorMessage}
    : {...error }
})

console.log(E) // const E = [  
               //   {
               //     type: 29,
               //     schema: {
               //       errorMessage: 'X error',
               //       type: 'number',
               //       [Symbol(TypeBox.Kind)]: 'Number'
               //     },
               //     path: '/x',
               //     value: '1',
               //     message: 'X error'                      // message mapped here
               //   },
               //   {
               //     type: 29,
               //     schema: {
               //       errorMessage: 'Y error',
               //       type: 'number',
               //       [Symbol(TypeBox.Kind)]: 'Number'
               //     },
               //     path: '/y',
               //     value: '2',
               //     message: 'Y error'                      // message mapped here
               //   },
               //   {
               //     type: 29,
               //     schema: {
               //       errorMessage: 'Z error',
               //       type: 'number',
               //       [Symbol(TypeBox.Kind)]: 'Number'
               //     },
               //     path: '/z',
               //     value: '3',
               //     message: 'Z error'                     // message mapped here
               //   }
               // ]

TypeBox keeps error functionality quite raw and doesn't make assumptions as to how users need their errors structured, and there are a number of ways you wrap up the above logic. However if you just need something to quickly remap errors for you, have a look at https://github.com/jtlapp/typebox-validators which provides custom error mapping plus several other validation features.

Hope this helps!
S

[sinclairzx81]

@JimSalies Hiya,

Might close off this issue. If you have any additional follow up questions, please feel free to respond on this thread.

All the best!
S

[JimSalies]

Thank you for this quick answer. It's exactly what I was looking for.
Given that I use react-hook-form to validate my forms, I will have to write a custom resolver.
This snippet is a good start to do it!