optional() does not create an optional property on an object

optional does not create an optional property on an object. It should create an optional property in order to match with TypeScript validation semantics.

const CustomText = object({
  name: string()
  age: optional(number())
})

// creates  a type like:
type UserType = {
  name: string
  age: number | undefined
}

// But it should create a type like this:
type UserType = {
  name: string
  age?: number | undefined
}

Alignment with TypeScript

The Superstruct type does not align with the TypeScript type it is returning.

As an example, this passes Superstruct validation:

describe("content-types", () => {
  it("should validate content-types", async () => {
    const User = object({
      name: string(),
      age: optional(number()),
    })
    assert({ name: "john" }, User)
  })
})

but fails the type number | undefined returned by Superstruct:

The red squiggles indicate the following error when hovered:

Use case

My use case is that I want to validate slate data types.

They are defined such that the bold property is optional. To be specific, they are optional(literal(true). In order to make sure my validations line up against my type definitions exactly, I use unit testing to make sure the two type are equal. Because the optional types show up as a union of the passed in type and undefined but do not add the ? to the property, they do not match and fail tests.

[thesunny]

@JakeElder @ianstormtaylor

This now has a PR: https://github.com/ianstormtaylor/superstruct/pull/390

[ianstormtaylor]

Ah interesting, that seems like a decent trade off I think. Seems pretty rare that you’d explicitly want a defined undefined value to me.