useEffect hook problem, use redux to get data from backend to frontend - redux

Question

Hello i am new to programming, and i have learn to use MERN to make a sign up,i have no issue with backend but when i tried to use redux ,i have this problem in the frontend
enter image description here
This is the code for the SignInScreen.js
import React, { useEffect, useState } from 'react'
import { useDispatch, useSelector } from 'react-redux'
import { Link, useLocation, useNavigate } from 'react-router-dom'
import { login } from '../actions/userAction'
export const SignInScreen = (props, history) => {
const navigate = useNavigate
const [email, setEmail] = useState('')
const [password, setPassword] = useState('')
const submitHandler = (e) => {
e.preventDefault()
dispatch(login(email, password))
}
const { search } = useLocation()
const redirectInUrl = new URLSearchParams(search).get('redirect')
const redirect = redirectInUrl ? redirectInUrl : '/'
const userlogin = useSelector((state) => state.userlogin)
const { userInfo, loading, error } = userlogin
const dispatch = useDispatch()
useEffect(() => {
if (userInfo) {
navigate(redirect)
}
}, [navigate, userInfo, redirect])
I dont know what wrong with the code,but i do know that it connected with the redux store which have reducer,action and constant..this is for the redux store.js
import { createStore, combineReducers, applyMiddleware, compose } from 'redux'
import thunk from 'redux-thunk'
import {
userLoginReducer,
} from './reducers/userReducer'
const userInfo = localStorage.getItem('userInfo')
? JSON.parse(localStorage.getItem('userInfo'))
: null
const initialState = {
userLogin: { userInfo },
}
const reducer = combineReducers({
userLogin: userLoginReducer,
})
const middleware = [thunk]
const store = createStore(
reducer,
initialState,
compose(applyMiddleware(...middleware))
)
export default store
This is for constant
export const USER_LOGIN_REQUEST = 'USER_LOGIN_REQUEST'
export const USER_LOGIN_SUCCESS = 'USER_LOGIN_SUCCESS'
export const USER_LOGIN_FAIL = 'USER_LOGIN_FAIL'
export const USER_LOGOUT = 'USER_LOGOUT'
this is userReducer.js
import {
USER_LOGIN_REQUEST,
USER_LOGIN_SUCCESS,
USER_LOGIN_FAIL,
USER_LOGOUT,
} from '../constants/userConstant'
function userLoginReducer(state = {}, action) {
switch (action.type) {
case USER_LOGIN_REQUEST:
return { loading: true }
case USER_LOGIN_SUCCESS:
return { loading: false, userInfo: action.payload }
case USER_LOGIN_FAIL:
return { loading: false, error: action.payload }
case USER_LOGOUT:
return {}
default:
return state
}
}
export userLoginReducer
and lastly for user.js
import Axios from 'axios'
import {
USER_LOGIN_REQUEST,
USER_LOGIN_SUCCESS,
USER_LOGIN_FAIL,
} from '../constants/userConstant'
const login = (email, password) => async (dispatch) => {
try {
dispatch({ type: USER_LOGIN_REQUEST })
const config = { headers: { 'Content-Type': 'application/json' } }
const { data } = await Axios.post(
'/api/users/login',
{ email, password },
config
)
dispatch({ type: USER_LOGIN_SUCCESS, payload: data })
localStorage.setItem('userInfo', JSON.stringify(data))
} catch (error) {
dispatch({
type: USER_LOGIN_FAIL,
payload:
error.response && error.response.data.message
? error.response.data.message
: error.message,
})
}
}
export login
I just want to get the data into the userInfo but it dont recognized them and said it is a TypeError..I hope u can help me with this..im using the redux latest version

Answer 1

The problem is in userLoginReducer. Each reducer should return a complete new copy of the store.
If you return just the changes, the object you return replaces the entire state.
For example in this code:
switch (action.type) {
case USER_LOGIN_REQUEST:
return { loading: true };
}
The state { userLogin: { userInfo } } will be replaced with { loading: true }. Then you will not have userLogin anymore in the state. That's why you get the error.
To overcome this problem, spread the previous state in returned object (for all actions):
switch (action.type) {
case USER_LOGIN_REQUEST:
return { ....state, loading: true }; // ...state copies exist state to the new copy of state
}
Note: To easily solve similar bugs in the future, I recommend to use redux devtools extension. It is a great extension for debugging and look at changes in redux store.

Answer 2

I have tried that but still cannot fix my problem,this is the rest of my signinScreen,js
import React, { useEffect, useState } from 'react'
import { useDispatch, useSelector } from 'react-redux'
import { Link, useLocation, useNavigate } from 'react-router-dom'
import { login } from '../actions/userAction'
export const SignInScreen = (props, history) => {
const navigate = useNavigate
const [email, setEmail] = useState('')
const [password, setPassword] = useState('')
const submitHandler = (e) => {
e.preventDefault()
dispatch(login(email, password))
}
const { search } = useLocation()
const redirectInUrl = new URLSearchParams(search).get('redirect')
const redirect = redirectInUrl ? redirectInUrl : '/'
const userlogin = useSelector((state) => state.userlogin)
const { userInfo, loading, error } = userlogin
const dispatch = useDispatch()
useEffect(() => {
if (userInfo) {
navigate(redirect)
}
}, [navigate, userInfo, redirect])
return (
<Container className="small-container">
<h1 className="my-3">Sign In</h1>
<Form onSubmit={submitHandler}>
<Form.Group className="mb-3" controlId="email">
<Form.Label>Email</Form.Label>
<Form.Control
type="email"
required
onChange={(e) => setEmail(e.target.value)}
/>
</Form.Group>
<Form.Group className="mb-3" controlId="password">
<Form.Label>Password</Form.Label>
<Form.Control
type="password"
required
onChange={(e) => setPassword(e.target.value)}
/>
</Form.Group>
<div className="mb-3">
<Button type="submit">Sign In</Button>
</div>
<div className="mb-3">
New Customer?{' '}
<Link to={`/signup?redirect=${redirect}`}>Create new account</Link>
</div>
</Form>
</Container>
)
}
it still show the same error like before,i have no idea to solve this