This TypeScript code snippet provides a function prefixKeys that allows you to prefix all the keys of an object or array of objects with a specified string. It also defines helper types to ensure type safety throughout the process.

prefixKeys.ts

// @author: https://github.com/jlucaso1
// @url: https://gist.github.com/jlucaso1/220756deaa75d130306bdece460d4c61

type ObjectUnion = Record<string, unknown> | unknown;

const isObject = (value: unknown): value is Record<string, unknown> =>
  typeof value === 'object' &&
  value !== null &&
  !(value instanceof RegExp) &&
  !(value instanceof Error) &&
  !(value instanceof Date);

interface Options<Prefix extends string = string> {
  prefix: Prefix;
}

export function prefixKeys<
  T extends ObjectUnion | ReadonlyArray<Record<string, unknown>>,
  Prefix extends string,
>(input: T, options: Options<Prefix>): PrefixKeys<T, Options<Prefix>> {
  if (Array.isArray(input)) {
    return input.map((element) => prefixKeys(element, options)) as PrefixKeys<
      T,
      Options<Prefix>
    >;
  }
  return transform(input, options) as PrefixKeys<T, Options<Prefix>>;
}

function transform(input: unknown, options: Options<string>): unknown {
  if (!isObject(input)) {
    return input;
  }

  const { prefix } = options;

  const result: Record<string, unknown> = {};
  for (const key in input) {
    if (Object.prototype.hasOwnProperty.call(input, key)) {
      const value = input[key];
      result[`${prefix}${key}`] = value;
    }
  }
  return result;
}

type PrefixKeys<
  T extends ObjectUnion | ReadonlyArray<Record<string, unknown>>,
  O extends Options<string>,
> =
  T extends ReadonlyArray<Record<string, unknown>>
    ? Array<PrefixKeys<T[number], O>>
    : T extends Record<string, unknown>
      ? {
          [K in keyof T as K extends string
            ? `${O['prefix']}${K}`
            : never]: T[K];
        }
      : T;