I am trying to get a state from context and initialize to new state. But the newly created state is not initializing. Help me out.
import { ProductsContext } from "../../../store/ProductsContext";
const EditVariant = () => {
let { id } = useParams();
const navigate = useNavigate();
const { getProductsById, singleProduct } = useContext(ProductsContext);
const [productName, setProductName] = useState(singleProduct.productName);
console.log(productName) // This is undefined
useEffect(() => {
getProductsById(id);
}, []);
return (
<Form
productName={productName}
setProductName={setProductName}
/>
</div>
);
};
export default EditVariant;
The Form component gets the undefined value. The value is not initializing properly.
You need to export your UserContext so it can be imported into the components that need it:
export const UserContext = React.createContext();
function App() {
const [name, setName] = useState('Name');
return (
<UserContext.Provider value={{ name, setName }}>
<Home />
</UserContext.Provider>
);
}
Afterward, you can import it into your desired component:
import { UserContext } '../../App'
function Home() {
const user = useContext(UserContext);
return (
<>
<label>Your name:</label>
<input type='text' onChange={e => user.setName(e.target.value)} />
<p>{user.name}</p>
</>
)
}
It might be because singleProduct.productName was undefiend in initial and get value later so you can simply set that in useEffect like this:
const { getProductsById, singleProduct } = useContext(ProductsContext);
const [productName, setProductName] = useState();
useEffect(() => {
if(singleProduct.productName){
setProductName(singleProduct.productName)
}
},[singleProduct])
Related
I have an input on the page, initially it is empty. I need to implement the following functionality: on page load, the component App fetches from localStorage a value of key appData and puts it in the input. That is, so that in the localStorage I write the value to the input and when reloading it is displayed in the input. How can i do this?
I need to use useEffect
import { useEffect, useState } from "react";
export default function App() {
const [userData, setUserData] = useState("");
useEffect(() => {
localStorage.setItem("Userdata", JSON.stringify(userData));
}, [userData]);
return (
<div>
<input value={userData} onChange={(e) => setUserData(e.target.value)}></input>
</div>
);
}
Use the change event to write to the localStorage, then use an init function in the useState hook.
import { useState } from 'react';
const loadUserData = () => localStorage.getItem('UserData') || '';
const saveUserData = (userData) => localStorage.setItem('UserData', userData);
export default const Application = () => {
const [ userData, setUserData ] = useState(loadUserData);
const handleUserDataUpdate = e => {
const userData = e.target.value;
setUserData(userData);
saveUserData(userData);
};
return <div>
<label htmlFor="testInput">Test Input</label>
<input id="testInput" value={ userData } onChange={ handleUserDataUpdate } />
</div>;
}
If you need an example using uncontrolled inputs, here is one using useEffect :
import { useEffect } from 'react';
const loadUserData = () => localStorage.getItem('UserData') || '';
const saveUserData = (userData) => localStorage.setItem('UserData', userData);
export default const Application = () => {
const inputRef = useRef();
useEffect(() => {
inputRef.current.value = loadUserData();
}, []); // initial load
const handleUpdateUserData = () => {
saveUserData(inputRef.current.value);
};
return <div>
<label htmlFor="testInput">Test Input</label>
<input ref={ inputRef } id="testInput" onChange={ handleUpdateUserData } />
</div>;
}
You can set a default value for the input inside state.
const [userData, setUserData] =
useState(JSON.parse(localStorage.getItem('Userdata')) || '');
So when the component mounts (after reload), the initial userData value is taken directly from the localStorage. If it's empty, the fallback value will be set ('').
Note: Make sure to add also the onChange handler to the input.
REACT.js:
Let say I have a home page with a search bar, and the search bar is a separate component file i'm calling.
The search bar file contains the useState, set to whatever the user selects. How do I pull that state from the search bar and give it to the original home page that
SearchBar is called in?
The SearchBar Code might look something like this..
import React, { useEffect, useState } from 'react'
import {DropdownButton, Dropdown} from 'react-bootstrap';
import axios from 'axios';
const StateSearch = () =>{
const [states, setStates] = useState([])
const [ stateChoice, setStateChoice] = useState("")
useEffect (()=>{
getStates();
},[])
const getStates = async () => {
let response = await axios.get('/states')
setStates(response.data)
}
const populateDropdown = () => {
return states.map((s)=>{
return (
<Dropdown.Item as="button" value={s.name}>{s.name}</Dropdown.Item>
)
})
}
const handleSubmit = (value) => {
setStateChoice(value);
}
return (
<div>
<DropdownButton
onClick={(e) => handleSubmit(e.target.value)}
id="state-dropdown-menu"
title="States"
>
{populateDropdown()}
</DropdownButton>
</div>
)
}
export default StateSearch;
and the home page looks like this
import React, { useContext, useState } from 'react'
import RenderJson from '../components/RenderJson';
import StateSearch from '../components/StateSearch';
import { AuthContext } from '../providers/AuthProvider';
const Home = () => {
const [stateChoice, setStateChoice] = useState('')
const auth = useContext(AuthContext)
console.log(stateChoice)
return(
<div>
<h1>Welcome!</h1>
<h2> Hey there! Glad to see you. Please login to save a route to your prefered locations, or use the finder below to search for your State</h2>
<StateSearch stateChoice={stateChoice} />
</div>
)
};
export default Home;
As you can see, these are two separate files, how do i send the selection the user makes on the search bar as props to the original home page? (or send the state, either one)
You just need to pass one callback into your child.
Homepage
<StateSearch stateChoice={stateChoice} sendSearchResult={value => {
// Your Selected value
}} />
Search bar
const StateSearch = ({ sendSearchResult }) => {
..... // Remaining Code
const handleSubmit = (value) => {
setStateChoice(value);
sendSearchResult(value);
}
You can lift the state up with function you pass via props.
const Home = () => {
const getChoice = (choice) => {
console.log(choice);
}
return <StateSearch stateChoice={stateChoice} giveChoice={getChoice} />
}
const StateSearch = (props) => {
const handleSubmit = (value) => {
props.giveChoice(value);
}
// Remaining code ...
}
Actually there is no need to have stateChoice state in StateSearch component if you are just sending the value up.
Hello and welcome to StackOverflow. I'd recommend using the below structure for an autocomplete search bar. There should be a stateless autocomplete UI component. It should be wrapped into a container that handles the search logic. And finally, pass the value to its parent when the user selects one.
// import { useState, useEffect } from 'react' --> with babel import
const { useState, useEffect } = React // --> with inline script tag
// Autocomplete.jsx
const Autocomplete = ({ onSearch, searchValue, onSelect, suggestionList }) => {
return (
<div>
<input
placeholder="Search!"
value={searchValue}
onChange={({target: { value }}) => onSearch(value)}
/>
<select
value="DEFAULT"
disabled={!suggestionList.length}
onChange={({target: {value}}) => onSelect(value)}
>
<option value="DEFAULT" disabled>Select!</option>
{suggestionList.map(({ id, value }) => (
<option key={id} value={value}>{value}</option>
))}
</select>
</div>
)
}
// SearchBarContainer.jsx
const SearchBarContainer = ({ onSelect }) => {
const [searchValue, setSearchValue] = useState('')
const [suggestionList, setSuggestionList] = useState([])
useEffect(() => {
if (searchValue) {
// some async logic that fetches suggestions based on the search value
setSuggestionList([
{ id: 1, value: `${searchValue} foo` },
{ id: 2, value: `${searchValue} bar` },
])
}
}, [searchValue, setSuggestionList])
return (
<Autocomplete
onSearch={setSearchValue}
searchValue={searchValue}
onSelect={onSelect}
suggestionList={suggestionList}
/>
)
}
// Home.jsx
const Home = ({ children }) => {
const [result, setResult] = useState('')
return (
<div>
<SearchBarContainer onSelect={setResult} />
result: {result}
</div>
)
}
ReactDOM.render(<Home />, document.getElementById('root'))
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.9.0/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.9.0/umd/react-dom.production.min.js"></script>
<div id="root"></div>
Just pass a setState to component
parent component:
const [state, setState] = useState({
selectedItem: ''
})
<StateSearch state={state} setState={setState} />
change parent state from child component:
const StateSearch = ({ state, setState }) => {
const handleStateChange = (args) => setState({…state, selectedItem:args})
return (...
<button onClick={() => handleStateChange("myItem")}/>
...)
}
I've got a bug with LocalStorage on react.js. I try to set a todo into it, but it doesn't load. This is the code:
import React, { useState, useRef, useEffect } from 'react';
import './App.css';
import TodoList from './TodoList';
const { v4: uuidv4 } = require('uuid');
const LOCAL_STORAGE_KEY = 'todoApp.todos'
function App() {
const [todos, setTodos] = useState([]);
const TodoNameRef = useRef()
useEffect(() => {
const storedTodos = JSON.parse(localStorage.getItem(LOCAL_STORAGE_KEY))
if (storedTodos) setTodos(storedTodos)
}, [])
useEffect(() => {
localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(todos))
}, [todos])
function HandleAddTodo(e){
const name = TodoNameRef.current.value
if (name==='') return
setTodos(prevTodos => {
return[...prevTodos, { id:uuidv4(), name:name, complete:false}]
})
TodoNameRef.current.value = null
}
return (
<>
<TodoList todos={todos}/>
<input ref={TodoNameRef} type="text" />
<button onClick={HandleAddTodo}>Add todo</button>
<button>clear todo</button>
<p>0 left todo</p>
</>
)
}
export default App;
This is TodoList.js
import React from 'react'
import Todo from './Todo';
export default function TodoList({ todos }) {
return (
todos.map(todo =>{
return <Todo key ={todo.id} todo={todo} />
})
)
}
And as last Todo.js:
import React from 'react'
export default function Todo({ todo }) {
return (
<div>
<label>
<input type="checkbox" checked={todo.complete}/>
{todo.name}
</label>
</div>
)
}
What the code has to do is load a todo into the local storage, and after refreshing the page reload it into the document. The code I implemented
I just started with react but I hope anyone can pass me the right code to make it work. If anyone need extra explenation, say it to me.
Kind regards, anonymous
Try to decouple your local storage logic into it's own react hook. That way you can handle getting and setting the state and updating the local storage along the way, and more importantly, reuse it over multiple components.
The example below is way to implement this with a custom hook.
const useLocalStorage = (storageKey, defaultValue = null) => {
const [storage, setStorage] = useState(() => {
const storedData = localStorage.getItem(storageKey);
if (storedData === null) {
return defaultValue;
}
try {
const parsedStoredData = JSON.parse(storedData);
return parsedStoredData;
} catch(error) {
console.error(error);
return defaultValue;
}
});
useEffect(() => {
localStorage.setItem(storageKey, JSON.stringify(storage));
}, [storage]);
return [storage, setStorage];
};
export default useLocalStorage;
And you'll use it just like how you would use a useState hook. (Under the surface it is not really more than a state with some side effects.)
const LOCAL_STORAGE_KEY = 'todoApp.todos'
function App() {
const [todos, setTodos] = useLocalStorage(LOCAL_STORAGE_KEY, []);
const handleAddTodo = event => {
setTodos(prevTodos => {
return[...prevTodos, {
id: uuidv4(),
name,
complete: false
}]
})
};
return (
<button onClick={HandleAddTodo}>Add todo</button>
);
}
You added the getItem and setItem methods of localStorage in two useEffect hooks.
The following code intializes the todo value in localStorage when reloading the page.
useEffect(() => {
localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(todos))
}, [todos])
So you need to set the todo value in HandleAddTodo event.
I edited your code and look forward it will help you.
import React, { useState, useRef, useEffect } from 'react';
import './App.css';
import TodoList from './TodoList';
const { v4: uuidv4 } = require('uuid');
const LOCAL_STORAGE_KEY = 'todoApp.todos'
function App() {
const [todos, setTodos] = useState([]);
const TodoNameRef = useRef()
useEffect(() => {
const storageItem = localStorage.getItem(LOCAL_STORAGE_KEY);
const storedTodos = storageItem ? JSON.parse(storageItem) : [];
if (storedTodos) setTodos(storedTodos)
}, []);
function HandleAddTodo(e){
const name = TodoNameRef.current.value;
if (name==='') return;
const nextTodos = [...todos, { id:uuidv4(), name:name, complete:false}];
setTodos(nextTodos);
localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(nextTodos));//replace todos to nextTodos
TodoNameRef.current.value = null
}
return (
<>
<TodoList todos={todos}/>
<input ref={TodoNameRef} type="text" />
<button onClick={HandleAddTodo}>Add todo</button>
<button>clear todo</button>
<p>0 left todo</p>
</>
)
}
export default App;
There is no need of adding the second useEffect.
You can set your local Storage while submitting in the handleTodo function.
Things you need to add or remove :
Remove the Second useEffect.
Modify your handleTodo function :
const nextTodos = [...todos, { id:uuidv4(), name:name,complete:false}];
setTodos(nextTodos);
localStorage.setItem(LOCAL_STORAGE_KEY, JSON.stringify(nextTodos));
Note: Make sure you won't pass todos instead of nextTodos as we know setTodos is an async function There might be a chance we are setting a previous copy of todos
I have this handleSubmit that returns me a key (verifyCode) that I should use in another component. How can I pass this verifyCode to another component?
const SendForm = ({ someValues }) => {
const handleSubmitAccount = () => {
dispatch(createAccount(id, username))
.then((response) => {
// I get this value from data.response, its works
const { verifyCode } = response;
})
.catch(() => {
});
};
return(
//the form with handleSubmitAccount()
)
}
export default SendForm;
The other component is not a child component, it is loaded after this submit step. But I don't know how to transfer the const verifyCode.
This is the view where the components are loaded, it's a step view, one is loaded after the other, I need to get the const verifyCode in FormConfirmation
<SendForm onSubmit={handleStepSubmit} onFieldSubmit={handleFieldSubmit} />
<FormConfirmation onSubmit={handleStepSubmit} onFieldSubmit={handleFieldSubmit} />
Does anyone know how I can do this?
You need to move up the state to a component that has both as children and then pass down a function that updates as a prop
import React from "react";
export default function App() {
const [value, setValue] = React.useState(0);
return (
<div className="App">
<Updater onClick={() => setValue(value + 1)} />
<ValueDisplay number={value} />
</div>
);
}
const Updater = (props) => <div onClick={props.onClick}>Update State</div>;
const ValueDisplay = (props) => <div>{props.number}</div>;
Check out the docs here
For more complex component structures or where your passing down many levels you may want to look into reactContext
import React from "react";
//Set Default Context
const valueContext = React.createContext({ value: 0, setValue: undefined });
export default function App() {
const [value, setValue] = React.useState(0);
return (
<div className="App">
{/** Pass in state and setter as value */}
<valueContext.Provider value={{ value: value, setValue }}>
<Updater />
<ValueDisplay />
</valueContext.Provider>
</div>
);
}
const Updater = () => {
/** Access context with hook */
const context = React.useContext(valueContext);
return (
<div onClick={() => context.setValue(context.value + 1)}>Update State</div>
);
};
const ValueDisplay = () => {
/** Access context with hook */
const context = React.useContext(valueContext);
return <div>{context?.value}</div>;
};
I want to pass a variable username from sibling1 component to sibling2 component and display it there.
Sibling1 component:
const sibling1 = ({ usernameData }) => {
// I want to pass the username value I get from input to sibling2 component
const [username, setUsername] = useState("");
const handleChange = event => {
setUsername(event.target.value);
};
return (
<Form.Input
icon='user'
iconPosition='left'
label='Username'
onChange={handleChange}
/>
<Button content='Login' onClick={handleClick} />
)
}
export default sibling1;
Sibling2 component:
export default function sibling2() {
return (
<h1> Here is where i want to display it </h1>
)
}
You will need to handle your userName in the parent of your siblings. then you can just pass setUsername to your sibling1, and userName to your sibling2. When sibling1 use setUsername, it will update your parent state and re-render your sibling2 (Because the prop is edited).
Here what it looks like :
const App = () => {
const [username, setUsername] = useState('Default username');
return (
<>
<Sibling1 setUsername={setUsername} />
<Sibling2 username={username} />
</>
)
}
const Sibling2 = ({username}) => {
return <h1> Helo {username}</h1>;
}
const Sibling1 = ({setUsername}) => {
return <button onClick={setUsername}>Set username</button>;
}
In parent of these two components create a context where you will store a value and value setter (the best would be from useState). So, it will look like this:
export const Context = React.createContext({ value: null, setValue: () => {} });
export const ParentComponent = () => {
const [value, setValue] = useState(null);
return (
<Context.Provider value={{value, setValue}}>
<Sibling1 />
<Sibling2 />
</Context.Provider>
);
Then in siblings you are using it like this:
const Sibling1 = () => {
const {setValue} = useContext(Context);
const handleChange = event => {
setValue(event.target.value);
};
// rest of code here
}
const Sibling2 = () => {
const {value} = useContext(Context);
return <h1>{value}</h1>;
}
best way: React Context + hooks
you can use React Context. take a look at this example:
https://codesandbox.io/s/react-context-api-example-0ghhy