How to normalize nested type transform in typescript?

March 12, 2023

I’m working on a type transforming library.
And I’m trying to transform a type into another type.

Given a simple example here.

interface Struct {
    a: {
        x: number;
        y: number;
    };
    b: string;
}

type OmitDeepX<T> = { [K in keyof T]: Omit<T[K], 'x'> };

export type TransformedStruct1 = OmitDeepX<Struct>;

VSCode output me this:

While the type is correct but as a user of this library I expected to see a normalized type like below

type TransformedStruct = {
   a: {
       y: number;
   };
   b: string;
}

And this is what I saw many times in other projects e.g. trpc, zod

But how could I achieve this?

>Solution :

Just wrap your type with this prettify helper

type Prettify<T> = T extends object ?  {[K in keyof T]: Prettify<T[K]>} : T

type OmitDeepX<T> = { [K in keyof T]: Omit<T, 'x'> };

type PrettyOmitDeep<T> = Prettify<OmitDeepX<T>>