lodash/internal/createForEach.js

define(['./bindCallback', '../lang/isArray'], function(bindCallback, isArray) {

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

  /**
   * Creates a function for `_.forEach` or `_.forEachRight`.
   *
   * @private
   * @param {Function} arrayFunc The function to iterate over an array.
   * @param {Function} eachFunc The function to iterate over a collection.
   * @returns {Function} Returns the new each function.
   */
  function createForEach(arrayFunc, eachFunc) {
    return function(collection, iteratee, thisArg) {
      return (typeof iteratee == 'function' && thisArg === undefined && isArray(collection))
        ? arrayFunc(collection, iteratee)
        : eachFunc(collection, bindCallback(iteratee, thisArg, 3));
    };
  }

  return createForEach;
});