Why is there no type t.object?

[jez9999]

When I'm making an interface I'd like to set a property to type t.object so that it ensures it is set to some object. Why does t.object not exist?

[jez9999]

@gcanti Is there a technical reason why t.object isn't there or is it just an oversight?

[phiresky]

I think the typescript object type did not exist yet when this library was created (introduced in TS 2.2: https://blog.mariusschulz.com/2017/02/24/typescript-2-2-the-object-type)

[jez9999]

Sounds like there's no good reason not to add it now then? Looks like it could pretty much copy/paste the string type and replace string with object.

[gcanti]

Indeed, when I first wrote io-ts it didn't exist.

The difference from { [key: string]: any } (i.e Dictionary) seems accessing by index which is not allowed. You can't even use typeof to refine

declare function f(x: { [key: string]: any }): void

f(1) // error
f('foo') // error
f(true) // error
f(null) // error
f(undefined) // error
f({}) // ok
f([]) // ok

declare function g(x: object): void

g(1) // error
g('foo') // error
g(true) // error
g(null) // error
g(undefined) // error
g({}) // ok
g([]) // ok

declare const x: { [key: string]: any }
declare const y: object

const xx = x['foo'] // ok
const yy = y['foo'] // error: Element implicitly has an 'any' type because type '{}' has no index signature.

const xxx = x.foo // ok
const yyy = y.foo // error: Property 'foo' does not exist on type 'object'

if (typeof y['foo'] !== 'undefined') { // error

}

[jez9999]

Can you add it?

[gcanti]

@jez9999 released

[jez9999]

Great!

[jez9999]

@gcanti Should a t.interface type be able to be used where a t.object is required? TypeScript says the types are incompatible but since an interface is always implemented by an object, shouldn't it count as a t.object?

[phiresky]

A number can also fulfill an interface like {toString:function}

…

On Nov 8, 2017 23:49, "Jeremy Morton" ***@***.***> wrote: @gcanti <https://github.com/gcanti> Should a t.interface type be able to be used where a t.object is required? TypeScript says the types are incompatible but since an interface is always implemented by an object, shouldn't it count as a t.object? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#86 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACMnYWy24_Tifwt0u1IJpHc30VT91Uk5ks5s0jAOgaJpZM4QVDpK> .

[jez9999]

Well is there a way for me to say "an interface fulfilled by an object" then? That's the kind of semantics I want here.