passing function from child to parent react code example

Example 1: pass element from child to parent react

Parent:

<div className="col-sm-9">
     <SelectLanguage onSelectLanguage={this.handleLanguage} /> 
</div>

Child:

handleLangChange = () => {
    var lang = this.dropdown.value;
    this.props.onSelectLanguage(lang);            
}

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>  
    );
}

Example 3: how to pass state from parent to child in react

class SomeParentComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {color: 'red'};
  }
  render() {
    return <SomeChildComponent color={this.state.color} />;
  }
}