如何在 Typescript 中循环引用 keyof？

Question

I have this following type:

type Test = {
    [K in keyof Test]: string
}

I want that K to be the key of Test. But I get this error: Type parameter 'K' has a circular constraint . How do I fix this?

UPDATE

This type is used as follows:

type Settings = {
    [K in keyof Settings]: string
}
type Items<T> = Record<keyof T, any>
function create(settings: Settings, data: Items<Settings>) {
    
}

create({
    name: "tt"
}, {
    name: "aaaa"
})

I want the type inference in data parameter in create

Answer 1

You could define Settings as a record of arbitrary keys (using the predefined type PropertyKey = string | number | symbol ), with string values:

type Settings = Record<PropertyKey, string>

keep Items the same

type Items<T> = Record<keyof T, any>

and add a generic parameter to create :

function create<S extends Settings>(settings: S, data: Items<S>) {
}

The resulting function will accept data objects that have the same keys as settings, and throw an error otherwise:

create({name: "tt", x: 'x'}, {name: 42, x: true}) // OK

create({name: "tt", x: 'x'}, {name: 42})
// ERROR: Property 'x' is missing in type '{ name: number; }' but required
// in type 'Items<{ name: string; x: string; }>

create({name: "tt", x: 'x'}, {name: 42, x: true, y: 1})
// ERROR: Object literal may only specify known properties, and 'y' does
// not exist in type 'Items<{ name: string; x: string; }>'.

TypeScript playground

Support for autocomplete on data properties can be achieved by adding a generic key parameter, which will allow partial data objects:

type Items<K extends PropertyKey> = Record<K, any>

function create<S extends Settings, K extends keyof S>(settings: S, data: Items<K> ) {
}

create({name: "tt", x: 'x'}, {name: 42, x: true}) // OK

create({name: "tt", x: 'x'}, {name: 42}) // OK: data can omit properties 

create({name: "tt", x: 'x'}, {name: 42, x: true, y: 1})
// ERROR: Object literal may only specify known properties, and 'y' does
// not exist in type 'Items<{ name: string; x: string; }>'.

TypeScript playground