GetByPath

Returns the type of the value at a specified path within the given object type. You can access nested object property types using dot notation.

If the object type has optional keys, you must use optional (?) path to access them. When accessing via an optional path, undefined is included in the returned type.

Setting the isUndefinable parameter to true also includes undefined in the returned type.

Interface

typescript

type GetByPath<
  T extends Record<PropertyKey, unknown>,
  P extends PropertyPath<T>,
  isUndefinable extends boolean = false
> = P extends `${infer LeftPath}.${infer RightPath}`
  ? LeftPath extends `${infer OptionalLeft}?`
    ? NonNullable<T[OptionalLeft]> extends Record<PropertyKey, unknown>
      ? GetByPath<NonNullable<T[OptionalLeft]>, RightPath, true>
      : never
    : T[LeftPath] extends Record<PropertyKey, unknown>
    ? GetByPath<T[LeftPath], RightPath, isUndefinable>
    : never
  : isUndefinable extends false
  ? T[P]
  : T[P] | undefined;

Type Parameters

Name	Constraint	Default	Description
T	Record<PropertyKey, unknown>	-	The object type to query
P	PropertyPath<T>	-	The property path expressed in dot notation
isUndefinable	boolean	false	Whether to include undefined in the return type for the path

Usage

Basic Case

typescript

import { GetByPath } from '@modern-kit/types';

type Example1 = GetByPath<{ a: { b: { c: 1 } } }, 'a'> // { b: { c: 1 } }
type Example2 = GetByPath<{ a: { b: { c: 1 } } }, 'a.b'> // { c: 1 }
type Example3 = GetByPath<{ a: { b: { c: 1 } } }, 'a.b.c'> // 1

Optional Property Case

typescript

import { GetByPath } from '@modern-kit/types';

type Example4 = GetByPath<{ a: { b?: { c: 1 } } }, 'a.b?.c'> // 1 | undefined

isUndefinable Case

typescript

import { GetByPath } from '@modern-kit/types';

type Example5 = GetByPath<{ a: { b: { c: 1 } } }, 'a.b.c', true> // 1 | undefined