Proposal: `PlainObject` about type-fest

[papb]

Your suggestion does not prevent nested things. Also what is the issue with arrays? I don't see any issue for a POJO to have an array, is there any?

I think the JsonObject provided by type-fest is probably what you want.

[Weakky]

I don't see any issue for a POJO to have an array, is there any?

The point here is not to prevent a POJO to have an array, the point is to prevent a POJO to be an array.

I think the JsonObject provided by type-fest is probably what you want.

JsonObject is not what I want as it doesn't allow classes and functions as values.

const obj: JsonObject = {
  a: () => {} // type error
}

Put differently, the PlainObject type achieves the same as what lodash.isPlainObject does, but at the type level.

_.isPlainObject(new Foo); // => false
const obj: PlainObject = new Foo // type error
 
_.isPlainObject([1, 2, 3]); // => false
const obj: PlainObject = [1, 2, 3] // type error
 
_.isPlainObject({ 'x': 0, 'y': 0 }); // => true
const obj: PlainObject = { 'x': 0, 'y': 0 } // working
 
_.isPlainObject(Object.create(null)); // => true
const obj: PlainObject = Object.create(null) // working

[Weakky]

Oh yeah, I re-read the issue and saw how it wasn't really clear given my wording. Sorry about that too 🙏

This is so surprising to me that I would actually think this is a bug in TypeScript. What is the explanation for this?

My theory is that { [props: string]: any } gets "transformed" into an object type, which allows both arrays and functions.

I didn't open a TS issue, but I found no question at all about this while googling so I ended up thinking it was more or less assumed correct by everyone 🙈

Is any the only type that does not give an error? Or is there another Foo that also does not give an error?

any is the only one I found too.

This was found by an actual bug in one of our open-source project. The code looked like this, see if you can spot the problem 🤦‍♂️:

function pluginHook(): { [props: string]: any } {
  const internalHook = () => {
    return {
      some: { value: true } 
    }
  }

  return internalHook
}

[papb]

Interesting, perhaps someone else can shed some light in this topic.

see if you can spot the problem

Forgot to call the function I guess 😅

[papb]

Oh, wow, I get it now!! The fact that { [props: string]: any } accepts () => {} itself was so unexpected to me that I didn't even parse correctly what you were saying. Sorry about that.

// This is not an error! Wow!!
const foo: { [props: string]: any } = () => {}

This is so surprising to me that I would actually think this is a bug in TypeScript. What is the explanation for this?

Out of curiosity, I tried the following:

type Primitive = string | number | boolean | null | undefined | symbol | bigint
type Foo<T> = { [x: string]: T }

const foo1: Foo<any> = () => { } // OK (????????)
const foo2: Foo<unknown> = () => { } // Error
const foo3: Foo<never> = () => { } // Error
const foo4: Foo<Primitive> = () => { } // Error
const foo5: Foo<() => void> = () => { } // Error

Is any the only type that does not give an error? Or is there another Foo<MagicalTypeHere> that also does not give an error?