Filter Null and Undefined Values from Nested Objects and Arrays in TypeScript

filter-null-and-undefined.ts

/**
 * Filters out null and undefined values from the given object or array, including nested objects and arrays.
 * @param {T} inputObj - The input object or array to filter.
 * @returns {Required<{ [K in keyof T]: NonNullable<T[K]> }>} - A new object or array with the same structure as the input, but with all null and undefined values removed.
 * @template T - The type of the input object or array, extending Record<string, any> or any[].
 */
export function filterNullAndUndefined<T extends Record<string, any> | any[]>(
  inputObj: T,
): Required<{ [K in keyof T]: NonNullable<T[K]> }> {
  if (typeof inputObj !== "object" || inputObj === null) {
    return inputObj as Required<{ [K in keyof T]: NonNullable<T[K]> }>;
  }

  const result: any = {};

  for (const key of Object.keys(inputObj) as Array<keyof T>) {
    const value = inputObj[key];

    if (value !== null && value !== undefined) {
      if (Array.isArray(value)) {
        result[key] = value.reduce((acc, item) => {
          if (item !== null && item !== undefined) {
            acc.push(filterNullAndUndefined(item));
          }
          return acc;
        }, []);
      } else if (typeof value === "object") {
        result[key] = filterNullAndUndefined(value);
      } else {
        result[key] = value;
      }
    }
  }

  return result as Required<{ [K in keyof T]: NonNullable<T[K]> }>;
}