Get a deep property of an object. Receive a path in the form of a dot-separated string which sould ignore any value that is not a valid property in the object tree.

getDeepValue.ts

export const getDeepValue = <
  T extends Record<string, any>,
  K extends string = string,
>(
  obj: T,
  path: DeepKey<T, K> | DeepKey<T, K>[],
): DeepReturn<T, K> => {
  const paths = Array.isArray(path) ? path : path.split('.');
  return paths.reduce<DeepReturn<T, K>>((acc, curr) => {
    return acc[curr];
  }, obj as DeepReturn<T, K>);
};

type ValidValues = string | number | object | Array<any> | undefined | null;

export type DeepKey<
  T extends Record<string, any>,
  K extends string = string,
> = K extends keyof T
  ? T[K] extends ValidValues
    ? K
    : never
  : K extends `${infer TKey}.${infer Rest}`
  ? T[TKey] extends ValidValues
    ? DeepKey<Exclude<T[TKey], undefined>, Rest> extends never
      ? never
      : K
    : never
  : never;

export type DeepReturn<T, K extends string = string> = K extends keyof T
  ? T[K]
  : K extends `${infer TKey}.${infer Rest}`
  ? TKey extends keyof T
    ? DeepReturn<Exclude<T[TKey], undefined>, Rest>
    : undefined
  : undefined;