connectHOC_subscription_1.js

function connectHOC(mapStateToProps, mapDispatchToProps) {
  return function wrapWithConnect(WrappedComponent) {
    class Connect extends Component {
      constructor(props, context) {
        super(props, context)
        this.store = context.store //access store from context
        //get parent's Subscription instance from context
        const parentSub = this.context.parentSub        
        //init its own Subscription instance based on the parent's Subscription
        this.subscription = new Subscription(this.store, parentSub, this.onStateChange.bind(this))
      }
      getChildContext() {
        //replace parentSub context for the child component with its own Subscription instance
        return {
          parentSub : this.subscription
        }
      }
      componentDidMount() {
        this.subscription.trySubscribe()
      }
      onStateChange() {
        this.setState({})
      }
      componentDidUpdate() {
        //after the current component get updated, go ahead and notify the nested subscription
        this.subscription.notifyNestedSubs()
      }
      ...
    }
    //the context exposed to container itself
    Connect.contextTypes = {
      store : storeShape,
      parentSub : subscriptionShape,
    }
    //replace the context of parentSub for the child component
    Connect.childContextTypes = { 
      parentSub: subscriptionShape,
    }
    return Connect
}