lodash/flatMap.js

define(['./_arrayMap', './_baseFlatten', './_baseIteratee'], function(arrayMap, baseFlatten, baseIteratee) {

  /**
   * Creates an array of flattened values by running each element in `array`
   * through `iteratee` and concating its result to the other mapped values.
   * The iteratee is invoked with three arguments: (value, index|key, array).
   *
   * @static
   * @memberOf _
   * @category Array
   * @param {Array} array The array to iterate over.
   * @param {Function|Object|string} [iteratee=_.identity] The function invoked per iteration.
   * @returns {Array} Returns the new array.
   * @example
   *
   * function duplicate(n) {
   *   return [n, n];
   * }
   *
   * _.flatMap([1, 2], duplicate);
   * // => [1, 1, 2, 2]
   */
  function flatMap(array, iteratee) {
    var length = array ? array.length : 0;
    return length ? baseFlatten(arrayMap(array, baseIteratee(iteratee, 3))) : [];
  }

  return flatMap;
});