React optionally controlled components

deriveStateFromProps.js

// @flow
const deriveStateFromProps = (nextProps: Object, prevState: Object) => {
  const derivedStateUpdate: Object = Object.keys(nextProps).reduce(
    (acc, key) => {
      if (nextProps[key] !== undefined && nextProps[key] !== prevState[key]) {
        return { ...acc, [key]: nextProps[key] };
      }

      return acc;
    },
    {},
  );

  if (Object.keys(derivedStateUpdate).length === 0) {
    return null;
  }

  return derivedStateUpdate;
};

class Component extends React.Component {
  static getDerivedStateFromProps(nextProps: Props, prevState: State) {
    return deriveStateFromProps(nextProps, prevState);
  }
  
  // ...
}