Extract React Component

App-1.js

// Before refactoring
import React, { Component } from "react";
import "./App.css";

class App extends Component {
  constructor(props) {
    super(props);
    this.state = { isToggleOn: true };

    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState(prevState => ({
      isToggleOn: !prevState.isToggleOn
    }));
  }

  render() {
    return (
      <div className="App">
        <button onClick={this.handleClick}>
          {this.state.isToggleOn ? "ON" : "OFF"}
        </button>
      </div>
    );
  }
}

export default App;

App-2.js

// After the refactoring
import React, { Component } from "react";
import "./App.css";
import { Button } from "./Button";

class App extends Component {
  constructor(props) {
    super(props);
    this.state = { isToggleOn: true };

    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState(prevState => ({
      isToggleOn: !prevState.isToggleOn
    }));
  }

  render() {
    return (
      <div className="App">
        <Button handleClick={this.handleClick} toggleOn={this.state.isToggleOn}/>
      </div>
    );
  }
}

export default App;

Button.js

// Extracted React component moved to a different file
import React, { PureComponent } from "react";
import * as PropTypes from "prop-types";

export class Button extends PureComponent {
  render() {
    return <button onClick={this.props.handleClick}>
      {this.props.toggleOn ? "ON" : "OFF"}
    </button>;
  }
}

Button.propTypes = {
  handleClick: PropTypes.func,
  toggleOn: PropTypes.bool
};