DeepGet

Resolves the value type at a given Path within T.

Returns unknown when any key in Path is not present in the corresponding level of T. An empty path resolves to T itself. A path segment that goes through an optional property keeps the result nullable (V | undefined) instead of degrading to unknown.

Available since v3.0.0

Import

import type { DeepGet } from '@helpers4/type';
// or, from the all-in-one package (same code, one install):
import type { DeepGet } from 'helpers4/type';

Type Definition

type DeepGet<T, Path extends readonly PropertyKey[]> =
  Path extends readonly []
    ? T
    : Path extends readonly [infer K, ...infer Rest extends readonly PropertyKey[]]
      ? K extends KeysOf<T>
        ? DeepGet<NonNullable<T>[K & keyof NonNullable<T>], Rest> | (undefined extends T ? undefined : never)
        : unknown
      : unknown

Examples

DeepGet

type Obj = { a: { b: { c: number } } };

DeepGet<Obj, ['a', 'b', 'c']> // => number
DeepGet<Obj, ['a', 'b']>      // => { c: number }
DeepGet<Obj, ['a', 'x']>      // => unknown
DeepGet<Obj, []>              // => Obj

type WithOptional = { a?: { b: number } };
DeepGet<WithOptional, ['a', 'b']> // => number | undefined

Source

View source on GitHub