How to rename interface keys?

Question

The task is to rename interface keys. Nesting level can vary. For example:

interface Foo {
  _id: string
  nested: {
    _id: string
    nested: {
      _id: number
    }
  }
}

// how to create another type that looks like type below?

type Bar = {
  id: string
  nested: {
    id: string,
    nested: {
      id: number
    }
  }
}

So, in this example I want to rename all _id keys to id, but type should remain the same.

Answer 1

You can try out the following type:

// T := your object type, K := key to change, R := new key name

type PickRename<T, K extends string, R extends string> =
  T extends object ? K extends keyof T ?
  ({ [P in R]: PickRename<T[K], K, R> } &
    { [P in Exclude<keyof T, K>]: PickRename<T[P], K, R> }) extends infer I ?
  { [PP in keyof I]: I[PP] } : never
  : T
  : T

Explanation using your example

1. If T is an object and key K ("_id") is contained, process the object, otherwise we just return T.

2. Drop the old property K (_"id") and add the renamed property R ("id"); process each property recursively further.

3. The extends infer I ? { [PP in keyof I]: I[PP] } : never part is just for DX/UX/formatting purposes to make the intersected type more readable.

/*
type T1 = {
    id: string;
    nested: {
        id: string;
        nested: {
            id: number;
        };
    };
}
*/
type T1 = PickRename<Foo, "_id", "id">

To expand this to multiple properties, you can have a look at possible PickRename implementations here.

Playground