pass a function down to a child component react code example

Example 1: pass setstate to child

//ChildExt component
class ChildExt extends React.Component {
    render() {
        return (<div><button onClick={() => this.props.handleForUpdate('someNewVar')}>Push me</button></div>
        )}
}
//Parent component
class ParentExt extends React.Component {
  constructor(props){
    super(props);
    this.state = {lol: false }
  }

    handleForUpdate(someArg){
            this.setState({lol: true});
      		console.log(someArg);
    }
  //Notice how we don't pass the arguments into the bind.this even though it does take an argument.
    render() {
        return (<ChildExt handleForUpdate={this.handleForUpdate.bind(this)} />)
    }
}

Example 2: pass props from parent to child react functional component

import React, { useState } from 'react';
import './App.css';
import Todo from './components/Todo'



function App() {
    const [todos, setTodos] = useState([
        {
          id: 1,
          title: 'This is first list'
        },
        {
          id: 2,
          title: 'This is second list'
        },
        {
          id: 3,
          title: 'This is third list'
        },
    ]);

return (
        <div className="App">
            <h1></h1>
            <Todo todos={todos}/> //This is how i'm passing props in parent component
        </div>
    );
}

export default App;


function Todo(props) {
    return (
        <div>
            {props.todos.map(todo => { // using props in child component and looping
                return (
                    <h1>{todo.title}</h1>
                )
            })}
        </div>  
    );
}