Is it possible to get action and state in store.subscribe?

[antonmedv]

I want to update my view in listener:

store.subscribe(() => {
    updateView(store.getState()); // Some DOM api calls.
});

But if it possible to get last action what triggered state change, i can do some think like this:

store.subscribe(() => {
    switch (action.type) {
        case UPDATE_TITLE:
            updateTitle(store.getState().some.title); // Optimize rendering of view. Only one DOM api call.
        break;
        default:
            updateView(store.getState()); // Some DOM api calls.
    }
});

Is it possible to get action and state in store.subscribe?

[sergey-lapin]

I made some hacking around this https://github.com/lapanoid/redux-remote/blob/master/src/createSubscribeOnStateStore.js but I am sure it is not the best way to do this. Waiting forward for @gaearon comment.

[gaearon]

This is not something we want to include by default. It's a hack around the paradigm, so if you really need it, please do so at your own risk.

Non-React Way

The easiest way is to have a reducer that remembers just the last action:

function lastAction(state = null, action) {
  return action;
}

Then you can use store.getState().lastAction, assuming you did something like

import { combineReducers, createStore } from 'redux';

const rootReducer = combineReducers({
  someReducer,
  someOtherReducer,
  lastAction // <-- use it!
});

const store = createStore(rootReducer);

store.subscribe(() => {
  console.log(store.getState().lastAction);
});

Still, this is not quite how Redux app is supposed to work, as this breaks the consistency in rendering.

React Way

If you want to optimize a React component, optimizations described in “Advanced Performance” is what you should be after; not this.

As a last resort you can always do side effects in componentWillReceiveProps:

componentWillReceiveProps(nextProps) {
  if (this.props.title !== nextProps.title) {
    // If somehow we're sure we can actually be faster than React at this. (not likely)
    findDOMNode(this).doSomethingWith(nextProps.title);
  }
}