JAVASCRIPT

context api react

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;

react context api

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>

React Context API

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

react context api

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>;
};

Context Api in react

// 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

Context Api in react

// 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

context api example in react

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} />;
  }
}

Context Api in react

// 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

context api react ts

export { TodosContext, default } from "./TodosContext";