React context

// ---------------- Parent.js 
import {createContext , useState} from "react";

let contextName = createContext( ) // you can optionally pass it a default value // it returns a "provider" object 

let Parent = () => {
    let [count , setCount] = useState()    // returns an [ state variable , state setter fn]. you can pass useState() a default value too
    				// the stateSetter function is async
    return ( 
        <div> 
            <contextName.Provider value={ {count , setCount } } >	// you can send multiple things across to the consumers by adding them in a single object
                <B/>
            </contextName.Provider> 
        </div>
    )
}

export {contextName};
export default Parent;


// file that consumes the context 
// --------- Child.js -----------

import {useContext} from "react";   // import the useContext hook that will allow you to actually use the created and imported context 
import {contextName } from "./Parent";   // import the particular context that you want to use 

let Child = () => {
    let value = useContext(contextName);
    return (
        <div> {value} </div>
    )
}

Source: grepper.com

React context

//React context allows us to pass data to our component tree without using props.
To use Context, we use the createContext function from React.
The created context includes a Provider and a Consumer property, which are each components.
We wrap the Provider around the component tree that we want to pass
the given value down.
Next, we place the Consumer in the component we want to consume the value.
import { createContext } from 'react';

const NameContext = createContext('');

function App() {
  return (
    <NameContext.Provider value="John Doe">
      <Body />
    <NameContext.Provider>
  );
} 

function Body() {
  return <Greeting />;
} 

function Greeting() {
  return (
    <NameContext.Consumer>
      {name => <h1>Welcome, {name}</h1>}
    //we got function with name argument which we will use
    </NameContext.Consumer>
  );
}

//using useContext hook 
 rewrite our example from earlier, using the useContext hook:

import { createContext, useContext } from 'react';

const NameContext = createContext('');

function App() {
  return (
    <NameContext.Provider value="John Doe">
      <Body />
    <NameContext.Provider>
  );
} 

function Body() {
  return <Greeting />;
} 

function Greeting() {
	const name = useContext(NameContext);
  //useContext with name of context
  return (
    <h1>Welcome, {name}</h1>
  );
}

Source: freecodecamp.org

Create a context in react

import React, { createContext, useReducer } from "react";
import reducer, { initialState } from "./reducer";

export let todoContext = createContext({});

export default function Provider({ children }) {

  const [state, dispatch] = useReducer(reducer, initialState);

  const values = {
    state,
    dispatch
  };

  return (
    <>
      <todoContext.Provider value={values}>
        {children}
      </todoContext.Provider>
    </>
  );
}

Source: codementor.io

React create context

import React from "react";
export const ThemeContext = React.createContext();

export default class Theme extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            mode: "dark",
            toggleMode: this.toggleMode
        }
    }
    toggleMode = () => {
        console.log('yes');
        this.setState({
            mode: this.state.mode === 'dark' ? 'light' : 'dark'
        });
    }
    render() {
        return (
            <ThemeContext.Provider value={this.state} >
                {this.props.children}
            </ThemeContext.Provider>
        )
    }
}

Source: grepper.com

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