Function flatten

lib/web/jshint.js:6454–6460

* Flattens a nested array. If `isDeep` is `true` the array is recursively * flattened, otherwise it is only flattened a single level. * * @static * @memberOf _ * @category Array * @param {Array} array The array to flatten. * @param {boolean} [isDeep] Specify a deep

(array, isDeep, guard)

     * // => [1, 2, 3, 4]
     */
    function flatten(array, isDeep, guard) {
      var length = array ? array.length : 0;
      if (guard && isIterateeCall(array, isDeep, guard)) {
        isDeep = false;
      }
      return length ? baseFlatten(array, isDeep) : [];
    }

    /**
     * Recursively flattens a nested array.