react redux -- `state.function[item]` syntax

Question

I'm trying to grok Redux's async Reddit API example code

But I'm having a really hard time understanding what's going on with these two functions:

//action
function shouldFetchPosts(state, subreddit) {
  const posts = state.postsBySubreddit[subreddit]
  if (!posts) {
    return true
  } else if (posts.isFetching) {
    return false
  } else {
    return posts.didInvalidate
  }
}

//reducer 
function postsBySubreddit(state = {}, action) {
  switch (action.type) {
    case INVALIDATE_SUBREDDIT:
    case RECEIVE_POSTS:
    case REQUEST_POSTS:
      return Object.assign({}, state, {
        [action.subreddit]: posts(state[action.subreddit], action)
      })
    default:
      return state
  }
}

In particuar, postsbySubreddit[subreddit]; I've never seen a function accessed with subscript notation, and doesn't that function require a parameter when it's called?

Sylvain · Accepted Answer · 2018-03-14 03:07:19Z

1

state.postsBySubreddit is not a function, it's the name of the attribute in the store where the postsBySubreddit reducer function stores it's state.

If you had a system with 3 reducers, r1(), r2() and r3() then the store would have 3 attributes where these reducers store their data: store.r1, store.r2 and store.r3.

answered Mar 14, 2018 at 3:07

Sylvain

19.3k26 gold badges103 silver badges148 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Daniel Thompson Over a year ago

Ahh I see, and the state of those attributes corresponds to the output of those functions I take it?

Collectives™ on Stack Overflow

react redux -- `state.function[item]` syntax

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related