Inspired by rails

Iterator prototype extensions

Object.defineProperty(Array.prototype, 'findAll', {
  enumerable: false,
  writable: false,
  value: condition => this.reduce((col, el, i) =>
    condition(el, i, this) ? [...col, el] : col, [])
});

Object.defineProperty(Array.prototype, 'exists', {
  enumerable: false,
  writable: false,
  value: condition => this.findIndex(condition) > -1,
});

// Type check in flow with

type ExtendedArray<T> =
  Array<T>
  & { exists: ((any, number, Array<any>) => boolean) => boolean }
  & { findAll: ((any, number, Array<any>) => boolean) => Array<any>};