shouldIkeepSomethingInReactState.js

function shouldIkeepSomethingInReactState() {
  if (canIcalculateItFromProps()) {
    // Don't duplicate data from props in state.
    // Calculate what you can in render() method.
    return false;
  }

  if (!amUsingItInRenderMethod()) {
    // Don't keep something in the state
    // if you don't use it for rendering.
    // for example, API subscriptions are
    // better off as custom private fields
    // or variables in external modules.
    return false;
  }
  // You can use React state from this!
  return true;

  // taken from: https://twitter.com/dan_abramov/status/749710501916139520
}