My question is why middlewareAPI can't use :
const middlewareAPI = {
getState: store.getState,
dispatch: dispatch
}
to replace the definition in the source code as below:
export default function applyMiddleware(...middlewares) {
return (createStore) => (reducer, preloadedState, enhancer) => {
const store = createStore(reducer, preloadedState, enhancer)
let dispatch = store.dispatch
let chain = []
const middlewareAPI = {
getState: store.getState,
dispatch: (...args) => dispatch(...args) // why not just use `dispatch: dispatch`
}
chain = middlewares.map(middleware => middleware(middlewareAPI))
dispatch = compose(...chain)(store.dispatch)
return {
...store,
dispatch
}
}
}
Anyone can tell me the difference ? Thanks.
It's a somewhat complicated combination of JS variable scoping/hosting, and needing to ensure that the passed-in dispatch method actually points back to the start of the middleware chain.
Please see the newly-added (and not yet published) Redux FAQ entry on why applyMiddleware uses a closure for more details.
Related
Usually in a thunk you'd wind up calling other actions:
const startRecipe = {type: "startRecipe"}
const reducer = (state, action) => {
if (action.type === "startRecipe") {
state.mode = AppMode.CookRecipe
}
}
const getRecipeFromUrl = () => async dispatch => {
const res = await Parser.getRecipeFromUrl(url)
dispatch(startRecipe)
}
With createAsyncThunk in redux toolkit, this isn't so straightforward. Indeed you can mutate the state from your resulting action in extraReducers:
export const getRecipeFromUrl = createAsyncThunk('getRecipeFromUrl',
async (url: string): Promise<RecipeJSON> => await Parser.getRecipeFromUrl(url)
)
const appStateSlice = createSlice({
name: 'app',
initialState: initialAppState,
reducers: {},
extraReducers: ({ addCase }) => {
addCase(getRecipeFromUrl.fulfilled, (state) => {
state.mode = AppMode.CookRecipe
})
}
})
But I also want to have non-async ways to start the recipe, which would entail a reducer in the slice:
reducers: {
startRecipe(state): state.mode = AppState.CookRecipe
},
To avoid writing the same code in two places I would love to be able to call the simple reducer function from the thunk handler. I tried simply startRecipe(state) and startRecipe (which had been destructured for ducks exporting so I’m fairly sure I was referring to the correct function) from the extraReducers case but it doesn't work.
My current solution is to define _startRecipe outside of the slice and just refer to that function in both cases
reducers: { startRecipe: _startRecipe },
extraReducers: builder => {
builder.addCase(getRecipeFromUrl.fulfilled, _startRecipe)
}
Is there a "better" way where you can define the simple action in your slice.reducers and refer to it from the thunk handler in extraReducers?
The second argument of the payloadCreator is thunkAPI (doc) from where you could dispatch the cookRecipe action.
interface ThunkApiConfig {
dispatch: AppDispatch,
state: IRootState,
}
export const getRecipeFromUrl = createAsyncThunk('getRecipeFromUrl',
async (url: string, thunkAPI: ThunkApiConfig): Promise<RecipeJSON> => {
await Parser.getRecipeFromUrl(url)
return thunkAPI.dispatch(cookRecipeActionCreator())
}
)
The idea of "calling a reducer" is the wrong approach, conceptually. Part of the design of Redux is that the only way to trigger a state update is by dispatching an action.
If you were writing the reducer using a switch statement, you could have multiple action types as cases that all are handled by the same block:
switch(action.type) {
case TypeA:
case TypeB: {
// common logic for A and B
}
case C: // logic for C
}
When using createSlice, you can mimic this pattern by defining a "case reducer" function outside of the call to createSlice, and pass it for each case you want to handle:
const caseReducerAB = (state) => {
// update logic here
}
const slice = createSlice({
name: "mySlice",
initialState,
reducers: {
typeA: caseReducerAB,
typeB: caseReducerAB,
}
extraReducers: builder => {
builder.addCase(someAction, caseReducerAB)
}
})
That sounds like what you described as your "current solution", so yes, that's what I would suggest.
I have a Redux app and it is working perfectly without any errors. Now I am trying to test it with Enzyme, Jest and Sinon:
it('calls constructor', () => {
sinon.spy(SavedVariantsComponent.prototype, 'constructor')
const store = configureStore()(STATE1)
wrapper = mount(<SavedVariantsComponent store={store} match={{ params: {} }} />)
expect(SavedVariantsComponent.prototype.constructor).toHaveProperty('callCount', 1)
})
In SavedVariantsComponent I have mapDispatchToProps:
const mapDispatchToProps = (dispatch, ownProps) => {
return {
onSubmit: (updates) => {
dispatch(updateSavedVariantTable(updates))
const { match, analysisGroup } = ownProps
const { familyGuid, variantGuid, tagArray, gene } = match.params
const familyGuids = familyGuid ? [familyGuid] : (analysisGroup || {}).familyGuids
const combineVariants = /combined_variants/.test(match.url)
dispatch(loadSavedVariants(combineVariants, familyGuids, variantGuid, tagArray, gene))
},
loadSavedVariants: (...args) => dispatch(loadSavedVariants(...args)),
}
}
And loadSavedVariants look like that:
export const loadSavedVariants = (combineVariants, familyGuids, variantGuid, tagArray, gene = '') => {
return (dispatch, getState) => {
...
...
and the error while running jest is:
Actions must be plain objects. Use custom middleware for async actions.
Which makes an HTTP Request that may not work in the current case. How to fix this error? I need to test that the constructor was called, but later on will also need to see how the inner Components are rendered, so need to have mount there. I suppose I am doing something wrong in testing and not in the real code since the latter is working without any errors, warnings or issues.
You probably need to configure your mock store to work with redux-thunk. See: https://github.com/dmitry-zaets/redux-mock-store#asynchronous-actions
import configureStore from 'redux-mock-store'
import thunk from 'redux-thunk'
const middlewares = [thunk] // add your middlewares like `redux-thunk`
const mockStore = configureStore(middlewares)
I have been wrestling with this problem and feel like I have a fundamental misunderstanding. I am using the redux-observable library in React which glues redux together with RxJS for handling asynchrony. My problem is that I have to handle a large upload and I want to show progress as the file is loaded.
The function uploadFileEpic needs to return an Observable<Action> to work with redux-observable. The uploadObservable represents the workflow that I want to accomplish. If I just return the uploadObservable the upload works but I don't get any handleUploadFileProgress actions from the progressSubscriber in the ajax call. Ideally the progressSubscriber would be adding elements to another observable that I could merge with uploadObservable. You see me trying to use merge here but the TypeScript compiler complains saying the return is not assignable to an ObservableInput.
I keep going in circles so I feel my understanding must be fundamentally off. I feel like I'm missing some simple RxJS magic here. Thanks for the help!
import { Observable, Observer, Subscriber, Subject, of } from 'rxjs';
import { ajax } from 'rxjs/ajax';
import { ofType } from 'redux-observable';
import { catchError, delay, map, mergeMap, tap, merge } from 'rxjs/operators';
import { apis } from '../../config';
export const enum ActionType {
InitialFileUpload
FileProgress
UploadFileSuccess
UploadFileFail
}
const handleInitialFileUpload = (file: File, timeLimit: number) => ({
type: ActionType.InitialFileUpload,
file,
timeLimit
})
const handleFileProgress = (file: File, percentComplete: number) => ({
type: ActionType.FileProgress,
file,
percentComplete
})
const handleUploadFileSuccess = (file: File, timeLimit: number) => ({
type: ActionType.UploadFileSuccess,
file,
timeLimit
})
const handleUploadFileFail = (file: File, timeLimit: number) => ({
type: ActionType.UploadFileFail,
file,
timeLimit
})
export const uploadFileEpic= action$ =>
action$.pipe(
ofType(ActionType.InitialFileUpload),
mergeMap((action: any) => {
const { file, timeLimit } = action;
const data = new FormData()
data.append('importFile', file, file.name)
data.append('timeLimit', timeLimit)
const progressSubject = new Subject();
const ajaxRequest = {
url: apis.gateway.run,
method: 'POST',
body: data,
headers: {},
progressSubscriber: Subscriber.create(
(e: ProgressEvent) => {
const percentComplete = Math.round((e.loaded / e.total) * 100)
console.log("Progress event")
progressSubject.next(handleUploadFileProgress(file, percentComplete))
}
)
}
const uploadObservable = ajax(ajaxRequest)
.pipe(
map(res => handleUploadFileSuccess(file)),
delay(SUCCESSFUL_UPLOAD_NOTIFICATION_LENGTH),
map(() => handleUploadFileRemove(file)),
catchError(error => of(handleUploadFileFail(file, error.response)))
)
return merge(uploadObservable, progressSubject)
}
)
)
You seem to be importing merge from rxjs/operators. There, merge is treated as an operator and thus returning an OperatorFunction. By importing from simply rxjs you get the static merge that correctly returns an Observable which will be flattened by your mergeMap.
I've read about bindActionCreators, i've compiled a resumen here:
import { addTodo,deleteTodo } from './actionCreators'
import { bindActionCreators } from 'redux'
function mapStateToProps(state) {
return { todos: state.todos }
}
function mapDispatchToProps(dispatch) {
return bindActionCreators({ addTodo, deleteTodo }, dispatch)
}
*short way
const mapDispatchToProps = {
addTodo,
deleteTodo
}
export default connect(mapStateToProps, mapDispatchToProps)(TodoApp)
another code use like this:
function mapDispatchToProps(dispatch) {
let actions = bindActionCreators({ getApplications });
return { ...actions, dispatch };
}
why previous code with bindActionCreators , don't need disptach parameter?
i've tried this way to get dispatch on this.props (but not working):
const mapDispatchToProps = (dispatch) => {
return bindActionCreators ({ appSubmitStart, appSubmitStop}, dispatch );
};
const withState = connect(
null ,
mapDispatchToProps,
)(withGraphqlandRouter);
why I had to change my old short way:
const withState = connect(
null ,
{ appSubmitStart, appSubmitStop}
)(withGraphqlandRouter);
in order to get this.props.dispatch()? because i neede to use dispatch for an isolated action creator inside a library with js functions. I mean before I don't needed use "bindActionCreators", reading this doc:
https://redux.js.org/api-reference/bindactioncreators
"The only use case for bindActionCreators is when you want to pass some action creators down to a component that isn't aware of Redux, and you don't want to pass dispatch or the Redux store to it."
I'm importing:
import { bindActionCreators } from 'redux';
import { connect } from 'react-redux';
what is the difference using redux pure, and react-redux?
really I need "bindActionCreators" in my new code? because without this i can't see this.props.dispatch()
UPDATE:
I've found this solutions to get this.props.dispatch working:
const mapDispatchToProps = (dispatch) => {
return bindActionCreators ({ appSubmitStart, appSubmitStop, dispatch }, dispatch ); // to set this.props.dispatch
};
does anyone can explain me? how i can send same distpach like a creator ?
First let's clear our minds regarding some of the key concepts here:
bindActionCreators is a util provided by Redux. It wraps each action creators to a dispatch call so they may be invoked directly.
dispatch is a function of the Redux store. It is used to dispatch actions to store.
When you use the object shorthand for mapState, React-Redux wraps them with the store's dispatch using Redux's bindActionCreators.
connect is a function provided by React-Redux. It is used to connect your component to the Redux store. When you connect your component:
It injects dispatch to your component only if you do not provide your customized mapDispatchToProps parameter.
Regarding what happened above to your code:
Component will not receive dispatch with customized mapDispatchToProps
In the code here:
const mapDispatchToProps = (dispatch) => {
return bindActionCreators(
{ appSubmitStart, appSubmitStop, dispatch }, // a bit problematic here, explained later
dispatch
); // to set this.props.dispatch
};
You are providing your own mapDispatch, therefore your component will not receive dispatch. Instead, it will rely on your returned object to contain the action creators wrapped around by dispatch.
As you may feel it is easy to make mistake here. It is suggested that you use the object shorthand directly, feeding in all the action creators your component will need. React-Redux binds each one of those with dispatch for you, and do not give dispatch anymore. (See this issue for more discussion.)
Writing customized mapState and inject dispatch manually
However, if you do need dispatch specifically alongside other action dispatchers, you will need to define your mapDispatch this way:
const mapDispatchToProps = (dispatch) => {
return {
appSubmitStart: () => dispatch(appSubmitStart),
appSubmitStop: () => dispatch(appSubmitStop),
dispatch,
};
};
Using bindActionCreators
This is exactly what bindActionCreators does. Therefore, you can simplify a bit by using Redux's bindActionCreators:
const mapDispatchToProps = (dispatch) => {
return bindActionCreators(
{ appSubmitStart, appSubmitStop }, // do not include dispatch here
dispatch
);
};
As mentioned above, the problem to include dispatch in the first argument is that it essentially gets it wrapped around by dispatch. You will be calling dispatch(dispatch) when you call this.props.dispatch.
However, bindActionCreators does not return the object with dispatch. It's passed in for it to be called internally, it does not give it back to you. So you will need to include that by yourself:
const mapDispatchToProps = (dispatch) => {
return {
...bindActionCreators({appSubmitStart, appSubmitStop}, dispatch),
dispatch
};
};
Hope it helped! And please let me know if anything here is unclear :)
I have made some changes to your code please try this
import * as Actions from './actionCreators'
import { bindActionCreators } from 'redux'
import { connect } from 'react-redux'
const mapStateToProps = (state)=>(
{
todos: state.todos
}
)
const mapDispatchToProps = (dispatch)=> (
bindActionCreators(Actions, dispatch)
)
export default connect(mapStateToProps, mapDispatchToProps)(TodoApp)
Hi I'm just working into Redux and currently I'm just confused about a redux syntax given in a Redux-Cheat-Sheet Redux Cheat Sheet from Egghead:
const actionLogger = ({dispatch, getState}) =>
(next) => (action) =>
{ console.log(action); return next(action) }
So my question is: What does this "chained" arrow functions behave like?
You can write it down as:
const actionLogger = function({dispatch, getState} /* this is store object */) {
return function(next) {
return function(action) {
console.log(action);
return next(action);
};
};
};
So basically chained arrow functions represent nested functions. It could be a bit confusing.
Detailed explanation how redux middleware works
If you want to use an arrow function:
const actionLogger = () => (dispatch, getState) => {
console.log(getState())
......
};