react-examples/avoid-mutation.htm at master · arvindpdmn/react-examples · GitHub

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<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>React Avoid Mutation</title>
</head>

<body>
    <div id="root"></div>

    <script src="https://unpkg.com/react@15/dist/react.js"></script>
    <script src="https://unpkg.com/react-dom@15/dist/react-dom.js"></script>
    <script src="https://unpkg.com/babel-standalone@6.15.0/babel.min.js"></script>

    <script type="text/jsx">
class ListOfWords extends React.PureComponent {
  render() {
    return <div>{this.props.words.join(',')}</div>;
  }
}

class WordAdder extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      words: ['marklar']
    };
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    // This section is bad style and causes a bug
    // because words is mutated and will compare equal
    // inside ListOfWords since it's a PureComponent
    //const words = this.state.words;
    //words.push('marklar');
    //this.setState({words: words});

    // Not mutating the words object here
    this.setState(prevState => ({
        words: prevState.words.concat(['marklar'])
    }));

    // ES6 syntax
    // this.setState(prevState => ({
    //    words: [...prevState.words, 'marklar'],
    // }));
  }

  render() {
    return (
      <div>
        <button onClick={this.handleClick}>Add</button>
        <ListOfWords words={this.state.words} />
      </div>
    );
  }
}

ReactDOM.render(
  <WordAdder />,
  document.getElementById('root')
);
    </script>
</body>

</html>