Sample React class and function component example which increment value on button click

ReactComponentExample.js

class Button extends React.Component {
    render() {
        return (
            <button onClick={() => this.props.onClickFunction(this.props.incrementValue)}>
                +{this.props.incrementValue}
            </button>
        );
    }
}

const Result = (props) => {
    return (
        <div>{props.counter}</div>
    );
}

class App extends React.Component {
    state = { counter: 0 };
    incrementCounter = (incrementValue) => {
        this.setState((prevState) => ({
            counter: prevState.counter + incrementValue
        }));
    }
    render() {
        return (
            <div>
                <Button incrementValue={1} onClickFunction={this.incrementCounter} />
                <Button incrementValue={2} onClickFunction={this.incrementCounter} />
                <Button incrementValue={3} onClickFunction={this.incrementCounter} />
                <Result counter={this.state.counter} />
            </div>
        );
    }
}

ReactDOM.render(<App />, mountNode)