Redux: Why is the reducer called three times?

[alesch]

In the counter example, the reducer is called three times upon start.
The same happens in todomvc example.
Why is this?

Thanks!

I added:

export default function counter(state = 0, action) {
  console.count('reducer');
   // ....

[gaearon]

combineReducers() probes your reducers to check for common mistakes before actually using them.
Don’t worry about it!

[alesch]

The reason I started looking into this is that in another project of mine, the reducer is called two times for every action. I am not using combineReducers there.

function defaultReducer (state, action) {
  return state;
}

function reducer (state, action) {
  return {
    data : defaultReducer(state.data, action),
    ui: {
      mainMenu: mainMenuReducer(state.ui.mainMenu, action)
    }
  }
}

[gaearon]

Please provide a runnable example to reproduce the issue, with expected and actual invocation count.
Otherwise it's hard to say.

[alesch]

I guess the question is: without using combineReducers, should my reducer be called once per action, and once on startup?
Or are there other invocations behind the scenes?

PS: Thanks a lot for Redux and for your time answering this questions. You rock!

[gaearon]

should my reducer be called once per action, and once on startup?

Reducer is called once on startup, and then once per every action.