lodash/transform.js

define(['./internal/arrayEach', './internal/baseCreate', './internal/baseForOwn', './internal/baseIteratee', './isArray', './isFunction', './isObject', './isTypedArray'], function(arrayEach, baseCreate, baseForOwn, baseIteratee, isArray, isFunction, isObject, isTypedArray) {

  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
  var undefined;

  /**
   * An alternative to `_.reduce`; this method transforms `object` to a new
   * `accumulator` object which is the result of running each of its own enumerable
   * properties through `iteratee`, with each invocation potentially mutating
   * the `accumulator` object. The iteratee is invoked with four arguments:
   * (accumulator, value, key, object). Iteratee functions may exit iteration
   * early by explicitly returning `false`.
   *
   * @static
   * @memberOf _
   * @category Object
   * @param {Array|Object} object The object to iterate over.
   * @param {Function} [iteratee=_.identity] The function invoked per iteration.
   * @param {*} [accumulator] The custom accumulator value.
   * @returns {*} Returns the accumulated value.
   * @example
   *
   * _.transform([2, 3, 4], function(result, n) {
   *   result.push(n *= n);
   *   return n % 2 == 0;
   * });
   * // => [4, 9]
   *
   * _.transform({ 'a': 1, 'b': 2, 'c': 1 }, function(result, value, key) {
   *   (result[value] || (result[value] = [])).push(key);
   * });
   * // => { '1': ['a', 'c'], '2': ['b'] }
   */
  function transform(object, iteratee, accumulator) {
    var isArr = isArray(object) || isTypedArray(object);
    iteratee = baseIteratee(iteratee, 4);

    if (accumulator == null) {
      if (isArr || isObject(object)) {
        var Ctor = object.constructor;
        if (isArr) {
          accumulator = isArray(object) ? new Ctor : [];
        } else {
          accumulator = baseCreate(isFunction(Ctor) ? Ctor.prototype : undefined);
        }
      } else {
        accumulator = {};
      }
    }
    (isArr ? arrayEach : baseForOwn)(object, function(value, index, object) {
      return iteratee(accumulator, value, index, object);
    });
    return accumulator;
  }

  return transform;
});