Accessing a reducer state from within another reducer - reactjs

Question

I have a reducer whereby I am retuning the appropriate state when an action is dispatched. Now I am calling an API at regular intervals so the result will trigger an action again and again. So what I want is that if the reducer state already has data then another reducer doesn't show the state as loading while the call is sent. It must maintain its loading state when receiving data the first time only. I hope I am able to explain it properly
Here are my code snippets
Loading state reducer
const loading = (state = false, action) => {
switch (action.type) {
case 'GET_AUDIT_DATA': // here I want to return true only when there is no data available
return true
case 'GET_AUDIT_DATA_RECEIVED':
return false
case 'GET_AUDIT_DATA_ERROR':
return false
default:
return state
}
}
Combining reducers
const allReducers = combineReducers({
auditData: AuditData,
auditLoading: AuditLoading,
modifiedOrders: ModifiedOrders
});
export default allReducers;
Reducer returning data on action triggered by superagent
const auditData = (state = [], action) => {
switch(action.type) {
case 'GET_AUDIT_DATA_RECEIVED':
console.log(action.data);
return action.data;
case 'GET_AUDIT_DATA_ERROR':
return action.err;
default :
return state;
}
}
export default auditData;
So initially the auditData doesn't contain any data, only after the first success call it returns the data. When this is called at the same time loading state reducer is called and it should return true in GET_AUDIT_DATA action only when the audit data reducer doesn't contain any data.
Also is returning just the current obtained data from auditData the right way to go or I should do it differently. Basically I want to overwrite the current data with the new one.

Answer 1

You can call getState() over a store to get the list of reducers and the current state inside the reducers.
Import the store into auditLoading (use store to get values. Don't mutate the store)
store.getState().auditLoading will give you the state of auditLoading reducer.
This approach is similar to the callback provided by redux-thunk. In which (dispatch, getState) => {} will be returned to the action.

Answer 2

The best way to proceed is to send to Loading state reducer an information to know if the other reducer already have data. To have at the end:
const loading = (state = false, action) => {
switch (action.type) {
case 'GET_AUDIT_DATA':
if(!action.dataAlreadyInitialized){
return true
}
case 'GET_AUDIT_DATA_RECEIVED':
return false
case 'GET_AUDIT_DATA_ERROR':
return false
default:
return state
}
}
You should have access from your action function to the application state and do:
dispatch({
type:'GET_AUDIT_DATA',
dataAlreadyInitialized: appState.auditData.length > 0
});

Answer 3

The accepted answer is fine (pass in the data length through the action) but can get laborious if it's a piece of information that is widely used. There is another solution that is sometimes preferable for something like 'current user' that might be used by every action.
According to the Redux FAQ https://redux.js.org/faq/reducers it is perfectly acceptable to add a third argument to the reducer function. I.e.:
Loading state reducer
const loading = (state = false, action, noData) => {
switch (action.type) {
case 'GET_AUDIT_DATA':
return noData
case 'GET_AUDIT_DATA_RECEIVED':
return false
case 'GET_AUDIT_DATA_ERROR':
return false
default:
return state
}
}
Combining reducers
Unfortunately it means we have to write code to combine the reducers, rather than use the combineReducers shortcut. But it's not too hard, you just call each reducer and create a new object if anything changed:
const allReducers = (state = null, action) => {
const auditData = AuditData(state?.auditData, action);
const auditLoading = AuditLoading(state?.auditLoading, action, !state?.auditData?.length);
const modifiedOrders = ModifiedOrders(state?.modifiedOrders, action);
return (auditData !== state?.auditData ||
auditLoading !== state?.auditLoading ||
modifiedOrders !== state?.modifiedOrders) ?
{ auditData, auditLoading, modifiedOrders } : state;
});
export default allReducers;
Notice the third argument passed to the AuditLoading reducer. No change is required to the other reducers, or to the code that invokes the action. Which is nice!

Answer 4

import store from '../../../redux/store'
console.log(store.getState().loginReducer.accessToken)
Through this statement we will get state of accessToken