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React context API tutorial

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M Hassan khan answered on January 4, 2021 Popularity 10/10 Helpfulness 1/10

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React context API tutorial

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/*
Context is a feature of React that allows us to create a piece of
state that any component within an area of your 
application can subscribe to.

------------- Why prop drilling is not ideal?----------

When props only have to be drilled through 1-2 components, 
prop drilling is a good strategy for making data available. 
However, when there are more layers to drill through, there may 
end up being many components that take in drilled props and pass 
down those props without ever using them. 
This can be a negative for two reasons:

1) It bloats your code and makes it harder to understand or 
use the middle components.
2) It causes middle components to re-render for changes 
to drilled props even if they don’t use those props themselves.
*/

/*
How do we use React Context API?
Create a new file then we start by creating a React context object, 
a named object created by the React.createContext() function. you
can import from react at the top.
*/

export const MyContext = createContext();

/*
Context objects include a .Provider property that is a 
React component. It takes in a 'value' prop to be stored in the context.
*/

<MyContext.Provider value="Hello world!"> 
   <ChildComponent />
</MyContext.Provider>


/*
That 'value' is available to all its 
descendent components (ChildComponet).

-----How ChildComponent can retrieve the context's value?-----

ChildComponent — can then retrieve the context’s value with 
React’s useContext() hook.

*/

import { useContext } from 'react';
import { MyContext } from './MyContext.js'
 
const ChildComponent = () => {
  const value = useContext(MyContext);
  return <p>{value}</p>;
}
// Renders <p>Hello, world!</p>

/*
The useContext() hook accepts the context object as an 
argument and returns the current value of the context. 
Rejoice — prop drilling that value is no longer needed!
*/

/*
---------What if we want to reuse the same context multiple times 
with different values????----------

Answer: A .Provider component may be reused with the same 
context multiple times in an application with different values. 
 For example, a component might render two .Provider 
 components that each receive a different value:
*/


const GreetingContext = React.createContext();
 
const ChildComponent = () => {
  const greeting = useContext(GreetingContext);
  return <h2>{greeting}</h2>
}
 
const MyComponent = () => {
  return (
    <>
      <GreetingContext.Provider value="bonjour le monde!">
        <ChildComponent />
      </GreetingContext.Provider>
      <GreetingContext.Provider value="hallo welt!">
        <ChildComponent />
      </GreetingContext.Provider>
    </>
  );
};




/*
----------- .Provider Wrappers -------------------

It’s common coding pattern for React applications to
create a “wrapper” component around a .Provider component.

 The wrapper component can provide a value  of its choosing,
 often one of its props or a string literal, 
 to the .Provider component.
 
 */


const ThemeContext = React.createContext();
 
const ThemedMessage = ({ children, theme }) => { //takes two props children and theme
  return (
    <ThemeContext.Provider value={theme}>
      This content is in {theme} mode!
      {children}
    </ThemeContext.Provider>
  );
};

/*
Wrapper components like ThemedMessage can then be used in 
place of a .Provider component to wrap children, means replace any 
calls to ContextName.Provider with this wrapper component.
*/

const MyComponent = () => {
  return (
    <ThemedMessage theme="dark"> // *Important*
    /*
     Make sure to use the *theme* prop rather than the 
     *value* prop of the .Provider.
    */
      Hooray!
    </ThemedMessage>
  )
};

/*
---------Updating Context----------------------

Now we have setup a wrapper component around a Context .Provider
component. Now we’re going to make use of that wrapper 
component by working with React state.

*/

/*
		------prop drilling method------
*/

const CounterApp = () => {
  const [count, setCount] = useState(0);
 
  return (
    <Counter count={count} setCount={setCount} />
  );
};

/*
		-------React Context method-------
        
 One common pattern is to have the context provide an object 
 containing both of those values. Child components that 
 consume the context can then use both (or either of) 
 the state and the state updater function.
*/

const CounterContext = React.createContext();
 
const CounterArea = ({ children, numProp }) => {
  const [count, setCount] = useState(numProp);
 
  return (
    <CounterContext.Provider value={{ count, setCount }}>
      {children}
    </CounterContext.Provider>
  );
};
 
const Counter = () => {
   //  destructuring to use those values from the object 
  //   returned by useContext().
  const { count, setCount } = useContext(CounterContext);

  return (
    <button onClick={() => setCount(count => count+1)}>
      {count}
    </button>
  );
};
 
const CounterApp = () => {
  return (
    <CounterArea>
      <Counter />
    </CounterArea>
  )
}

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Source: Grepper

Tags: api javascript react-context

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Contributed on Dec 31 2022

M Hassan khan

0 Answers Avg Quality 2/10

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setup context api

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//# Contect.js 
import { useEffect, useState, createContext } from "react";

export const CharityContext = createContext();

export const CharityContextProvider = ({ children }) => {
  const loki = "chaulagain";
  return <CharityContext.Provider value={{ loki }}>{children}</CharityContext.Provider>;
};

//# app.js
import { CharityContextProvider } from "../context/Context";

function MyApp({ Component, pageProps }: AppProps) {
  return (
    <CharityContextProvider>
      <Component {...pageProps} />
    </CharityContextProvider>
  );
}

export default MyApp;

//# fetch data in any file
import React, { useContext } from "react";
import { CharityContext } from "../context/Context";

function Index() {
  const { loki } = useContext(CharityContext);
  console.log(loki); //-->Result:Chaulagain
  return <div>Index</div>;
}

export default Index;

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Source: Grepper

Tags: api

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Contributed on Oct 29 2022

Loki Chaulagain

0 Answers Avg Quality 2/10

React Context API

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/*
The React Context API uses a Provider and Consumer pattern to 
share data throughout an application. The provider role 
is played by a React componentthat makes data available to 
its descendant components. 

When one of those descendants accesses the shared data, 
it becomes a consumer.

To use the React Context API, we start by creating a React 
context object, a named object created by the
React.createContext() function.
*/

const MyContext = React.createContext();

/*
Context objects include a .Provider property that is 
a React component. It takes in a value prop to be stored
in the context.
*/

<MyContext.Provider value="Hello world!">
   <ChildComponent />
</MyContext.Provider>
/*
That value — in this case, the string "Hello world!" — is 
available to all its descendent components. Descendent 
components — in this case, ChildComponent — can then retrieve 
the context’s value with React’s useContext() hook.
*/

import { useContext } from 'react';
import { MyContext } from './MyContext.js'
 
const ChildComponent = () => {
  const value = useContext(MyContext);
  return <p>{value}</p>;
}
// Renders <p>Hello, world!</p>

/*
The useContext() hook accepts the context object as an 
argument and returns the current value 
of the context. Rejoice — prop drilling that value is 
no longer needed!

Note: If a component attempts to use a context that 
isn’t provided by one of its ancestors, useContext() will return null.
*/

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Source: Grepper

Tags: api

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Contributed on Dec 30 2022

M Hassan khan

0 Answers Avg Quality 2/10

context api react

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import React from "react";
// 1. Create context - storing values
export const CartContext = React.createContext();
// CartContext.Provider
// this is you create that context box
// Provider

export function CartContextProvider({ children }) {
  const [cartCount, setCartCount] = React.useState(0);
  const handleCartUpdate = (val) => {
    setCartCount(cartCount + val);
  };
  const handleDec=(val)=>{

    setCartCount(cartCount + val);
  }

  return (
    <CartContext.Provider value={{ cartCount, handleCartUpdate,handleDec }}>
      {children}
    </CartContext.Provider>
  );
}

=====================navbar.jsx
import React from "react";
import { CartContext } from "../Context/CardContexr";

const Navbar = () => {
  const { cartCount } = React.useContext(CartContext);
  const{handleCartUpdate}= React.useContext(CartContext)
//   const { theme } = React.useContext(ThemeContext);

  return <>
  
  <h1 >Cart Count : {cartCount}</h1>

  <button onClick={()=>{handleCartUpdate(1)}} >change</button>
  </>
};

export default Navbar;

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Source: Grepper

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Contributed on Aug 26 2022

Binod Nayak

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react context api

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DEFINITION::::::
Context provide a way to pass data through the component tree without 
having to pass down manually at every level

HOW TO USE::::::
DECLARATION:::
	const MyContext = React.createContext()
Creating a new Context for each unique piece of data that needs to be available
throughout your component data
	const LocaleContext = React.createContext()
Properties of LocaleContext --------
	LocaleContext.Provider
    LocaleContext.Consumer

What is a Provider 
	Allows us to "declare the data that we want available throughout our
	component tree"

What is a Consumer
	Allows "any component in the tree that needs that data to be able to 
    subscibe to it"

How to use Provider	
	<MyContext.Provider value={data}>
      <App />
    </MyContext.Provider>

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Source: Grepper

Tags: api

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Contributed on Jan 04 2021

KROTUS

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React Context API

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import React, { useState } from 'react'

const GlobalStateContext = React.createContext({ })

export const GlobalStateProvider = ({ children }) => {
    const [config, setConfig] = useState({
        projectInfo: ''
    })
    const [projectFile, setProjectFile] = useState('./test.cpp')
    const [executionState, setExecutionState] = useState("NoProject")

    return (
        <GlobalStateContext.Provider
            value={{
                executionState,
                config,
                projectFile,
                setExecutionState,
                setConfig,
                setProjectFile,
            }}
        >
            {children}
        </GlobalStateContext.Provider>
    )
}

export default GlobalStateContext

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Source: stackoverflow.com

Tags: api

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Contributed on Jan 10 2022

Noob Learner

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Context Api in react

Comment

// In App.js 
<NoteState>
	components where you want to use this context which you created    
</NoteState>

// In NoteContext.js 
import { createContext } from "react";

const NoteContext = createContext();

export default NoteContext;

// In NoteState.js or whatever name you want to give
import NoteContext from "./NoteContext";

const NoteState = (props)=>{
  // you can also pass state here also or functions also 
    const user = {
        name: "Gourav Khurana",
        age: 19,
        caast: "General"
    }
    return (
        <NoteContext.Provider value={user}>
            {props.children}
        </NoteContext.Provider>
    )
}
export default NoteState;


This is all about Context API how to create it and add it to Components 

Now how to use it in the Components :- 
  
import React, { useContext } from 'react';
import NoteContext from "../contexts/notes/NoteContext";

const About = () => {
    const contextValue = useContext(NoteContext);
    return (
       you can simply use here. 
    )
}

export default About

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Source: Grepper

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Contributed on Jan 12 2022

Coding is fun

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react context api

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import { createContext, useContext, useReducer } from "react";

const Actions = {
	SET_ITEMS: "SET_ITEMS",
};

const reducer = (state, action) => {
	if (action.type === Actions.SET_ITEMS) {
		return { ...state, items: action.payload };
    }

	return state;
};

const initialState = {
	items: []
};

const SimpleContext = createContext(initialState);
export const useSimpleContext = () => useContext(SimpleContext);
export const SimpleProvider = ({ children }) => {
	const [state, dispatch] = useReducer(reducer, initialState);

	function setItems(items) {
		dispatch({ type: Actions.SET_ITEMS, payload: items });
	}

	return <SimpleContext.Provider value={{ state, setItems }}>{children}</SimpleContext.Provider>;
};

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Source: Grepper

Tags: api

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Contributed on Mar 19 2022

Red Team

0 Answers Avg Quality 2/10

Context Api in react

Comment

// In App.js 
<NoteState>
	components where you want to use this context which you created    
</NoteState>

// In NoteContext.js 
import { createContext } from "react";

const NoteContext = createContext();

export default NoteContext;

// In NoteState.js or whatever name you want to give
import NoteContext from "./NoteContext";

const NoteState = (props)=>{
  // you can also pass state here also or functions also 
    const user = {
        name: "Gourav Khurana",
        age: 19,
        caast: "General"
    }
    return (
        <NoteContext.Provider value={user}>
            {props.children}
        </NoteContext.Provider>
    )
}
export default NoteState;


This is all about Context API how to create it and add it to Components 

Now how to use it in the Components :- 
  
import React, { useContext } from 'react';
import NoteContext from "../contexts/notes/NoteContext";

const About = () => {
    const contextValue = useContext(NoteContext);
    return (
       you can simply use here. 
    )
}

export default About

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Source: Grepper

Tags: api

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Contributed on Jan 12 2022

Coding is fun

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Context_api

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import React, { useContext } from "react";
import CountContext from "./context";

const Child = () => {
  const context = useContext(CountContext);
  const { countHandler } = context;

  return (
    <div>
      <button onClick={countHandler}>Increment</button>
    </div>
  );
};
export default Child;

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Source: hackernoon.com

Tags: whatever whateve

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Contributed on Dec 19 2022

Grumpy Goose

0 Answers Avg Quality 2/10

context api example in react

Comment

class App extends React.Component {
  render() {
    return <Toolbar theme="dark" />;
  }
}

function Toolbar(props) {
  // The Toolbar component must take an extra "theme" prop
  // and pass it to the ThemedButton. This can become painful
  // if every single button in the app needs to know the theme
  // because it would have to be passed through all components.
  return (
    <div>
      <ThemedButton theme={props.theme} />
    </div>
  );
}

class ThemedButton extends React.Component {
  render() {
    return <Button theme={this.props.theme} />;
  }
}

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Source: reactjs.org

Tags: api

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Contributed on Jun 08 2022

Paras

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React context API tutorial

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