Function flatten

modules/core/src/utils/flatten.ts:17–27

(
  array: T | NestedArray<T>,
  filter: (element: T) => boolean = () => true
)

 * @return Returns the new flattened array (new array or `result` if provided)
 */
export function flatten<T>(
  array: T | NestedArray<T>,
  filter: (element: T) => boolean = () => true
): T[] {
  // Wrap single object in array
  if (!Array.isArray(array)) {
    return filter(array) ? [array] : [];
  }
  // Deep flatten and filter the array
  return flattenArray(array, filter, []);
}

/** Deep flattens an array. Helper to `flatten`, see its parameters */
function flattenArray<T>(array: NestedArray<T>, filter: (element: T) => boolean, result: T[]): T[] {