Function flatten

lodash.js:7420–7423

* Flattens `array` a single level deep. * * @static * @memberOf _ * @since 0.1.0 * @category Array * @param {Array} array The array to flatten. * @returns {Array} Returns the new flattened array. * @example * * _.flatten([1, [2, [3, [4]], 5]]);

(array)

     * // => [1, 2, [3, [4]], 5]
     */
    function flatten(array) {
      var length = array == null ? 0 : array.length;
      return length ? baseFlatten(array, 1) : [];
    }

    /**
     * Recursively flattens `array`.