Accessing the "final" schema and extracting it's rules

Let’s say I have the following schema (one of the examples in Yup’s documentation):

let schema = object({
  isSpecial: boolean(),
  isBig: boolean(),
  count: number().when(['isBig', 'isSpecial'], {
    is: true, // alternatively: (isBig, isSpecial) => isBig && isSpecial
    then: yup.number().min(5),
    otherwise: yup.number().min(0),
  }),
});

const result = schema.validateSync({
  isBig: true,
  isSpecial: true,
  count: 10,
});

The count min value depends on the value of isBig. That value is decided at runtime, when calling validate(). Is there a way I can somehow access the “final” schema and programatically check what Yup decided to enforce?

Something like:

const { result, finalSchema } = schema.validateSync({
  isBig: true,
  isSpecial: true,
  count: 10,
});

console.log(finalSchema.count.min) // 5

[jakobsandberg]

@alexandernst as mentioned above, schema.resolve() won’t resolve nested schemas. We must instead resolve the nested schema, count in this case, via yup.reach().

Now that we’re resolving at the nested schema, we’ll need to provide a parent object to schema.resolve() in order for this nested schema to access the values of its siblings.

const resolved = yup.reach(schema, 'count').resolve({
  parent: {
    isBig: true,
    isSpecial: true,
    count: 10
  }
});

[jakobsandberg]

It would be nice if Yup could resolve nested schemas by default though.

Yes, that would be handy. Fortunately, Yup provides a good API for extending functionality like this.

For example, you can add a resolveDeep method to your schemas that traverses the schema and resolves each node in a similar manner to the workaround I posted above.

yup.addMethod(yup.mixed, 'resolveDeep', function(values) {
  // traverse schema and resolve each node 
})