I'm trying to understand the connect method of react-redux, and the functions it takes as parameters. In particular mapStateToProps()
.
The way I understand it, the return value of mapStateToProps
will be an object derived from state (as it lives in the store), whose keys will be passed to your target component (the component connect is applied to) as props.
This means that the state as consumed by your target component can have a wildly different structure from the state as it is stored on your store.
Q: Is this OK?
Q: Is this expected?
Q: Is this an anti-pattern?
Yes, it is correct. Its just a helper function to have a simpler way to access your state properties
Imagine you have a posts
key in your App state.posts
state.posts //
/*
{
currentPostId: "",
isFetching: false,
allPosts: {}
}
*/
And component Posts
By default connect()(Posts)
will make all state props available for the connected Component
const Posts = ({posts}) => (
<div>
{/* access posts.isFetching, access posts.allPosts */}
</div>
)
Now when you map the state.posts
to your component it gets a bit nicer
const Posts = ({isFetching, allPosts}) => (
<div>
{/* access isFetching, allPosts directly */}
</div>
)
connect(
state => state.posts
)(Posts)
mapDispatchToProps
normally you have to write dispatch(anActionCreator())
with bindActionCreators
you can do it also more easily like
connect(
state => state.posts,
dispatch => bindActionCreators({fetchPosts, deletePost}, dispatch)
)(Posts)
Now you can use it in your Component
const Posts = ({isFetching, allPosts, fetchPosts, deletePost }) => (
<div>
<button onClick={() => fetchPosts()} />Fetch posts</button>
{/* access isFetching, allPosts directly */}
</div>
)
An example of an actionCreator: deletePost
const deletePostAction = (id) => ({
action: 'DELETE_POST',
payload: { id },
})
So, bindActionCreators
will just take your actions, wrap them into dispatch
call. (I didn't read the source code of redux, but the implementation might look something like this:
const bindActionCreators = (actions, dispatch) => {
return Object.keys(actions).reduce(actionsMap, actionNameInProps => {
actionsMap[actionNameInProps] = (...args) => dispatch(actions[actionNameInProps].call(null, ...args))
return actionsMap;
}, {})
}