froebel/map.mjs

TypeScript utility library

/**
 * Map over `data`. `data` can be a regular object, a `Map`, a `Set`, or an
 * array.
 *
 * @example
 * ```
 * // -> { a: 1, b: 2 }
 * map({ a: '1', b: '2' }, (key, value) => [key, parseInt(value)])
 * ```
 *
 * @example
 * ```
 * // -> Map([ [2, 1], [4, 3] ])
 * map(new Map([ [1, 2], [3, 4] ]), (key, value) => [key + 1, value - 1])
 * ```
 */
const map = (data, cb) => {
  if (typeof data !== "object" || data === null) {
    throw new TypeError(`cannot map over ${data}`);
  }

  if (data instanceof Map) {
    return new Map([...data].map(([key, value]) => cb(key, value)));
  }

  if (data instanceof Set) {
    return new Set([...data].map(el => cb(el)));
  }

  if (Array.isArray(data)) {
    return data.map(el => cb(el));
  }

  return Object.fromEntries(Reflect.ownKeys(data).map(key => cb(key, data[key])));
};

export default map;