Typescript 窄 {[key: string]: T} 到 object 文字

Question

I would like to write a function that enforces an object to be of type {[key: string]: T} and returns an object literal of the provided argument.

For example, if I have the following type A:

interface A{
  a: string,
  b: number
}

I would like to have a function B that takes an object with properties, all of type A , and returns the provided object with properties accessible using dot notation.

My current function is this:

const B = (arg: {[key: string]: A}) => arg;

But when I call it like so:

const c = B({
  a: {
    a: "test",
    b: 1
  }
})

I can't access the property a with dot notation, like c.a .

How can I make it so that function B returns a literal type based on what it receives so that I can access properties with dot notation?

Answer 1

You need to use a generics .

Typescript rpl

interface A{
  a: string,
  b: number
}

const B = <T extends Record<string, A>>(arg: T): T => arg;

const c = B({
  a: {
    a: "test",
    b: 1
  }
})

console.log(c.a.a)