Extending Flow types

Flow.js

// extending existing type
type SelectOption = {
  value: string,
  label: string
}

const option1: SelectOption = {
  value: 'value',
  label: 'label'
}

type DurationSelectOption = {
  ...SelectOption,
  value: '1m' | '1w' | '1d'
}

const option2: DurationSelectOption = {
  value: '1m',
  label: 'label'
}

// if it's in flow/dom.js
declare interface Navigator extends Navigator {
  mediaDevices: MediaDevicesType;
}