TypeScript getNestedObjectProperty

getNestedObjectProperty.ts

type JoinPath<A extends readonly string[]> = A extends readonly [infer K]
  ? K extends string
    ? K
    : never
  : A extends readonly [infer K, ...infer Rest]
    ? K extends string
      ? Rest extends readonly string[]
        ? `${K}.${JoinPath<Rest>}`
        : never
      : never
    : never;

type SplitPath<A extends string> = A extends `${infer K}.${infer Rest}`
  ? [K, ...SplitPath<Rest>]
  : A extends string
    ? readonly [A]
    : never;

type NestedObjectPath<T, Path extends readonly string[] = []> = T extends object
  ?
      | {
          [K in keyof T & string]: T[K] extends object ? NestedObjectPath<T[K], [...Path, K]> : JoinPath<[...Path, K]>;
        }[keyof T & string]
      | JoinPath<Path>
  : never;
    
type NestedObjectValue<T, Path extends NestedObjectPath<T>> = [Path] extends [never]
  ? T
  : SplitPath<Path> extends readonly [infer K, ...infer Rest]
    ? K extends keyof T
      ? Rest extends readonly string[]
        ? NestedObjectValue<T[K], JoinPath<Rest> & NestedObjectPath<T[K]>>
        : never
      : never
    : never;

function getNestedObjectProperty<T, const Path extends NestedObjectPath<T>>(
  obj: T,
  path: Path,
): NestedObjectValue<T, Path> {
  return path.split('.').reduce((o: any, i) => o[i], obj);
}

const kekw = getNestedObjectProperty({ a: { b: { c: 1 } } }, 'a.b.c');