ReactJs app crashes with error "Consider adding error boundaries to your tree"

Question

Trying to Build Random quote api app with React. When first time app loads on Button Click it generates the random quote. But on Second Click App Crashes with "Error occured in App Component" "Consider adding an error boundary to your tree to customize error handling behavior.

class App extends React.Component {
  state = {
    quotes: null
  };
  componentDidMount() {
  fetch("https://gist.githubusercontent.com/camperbot/5a022b72e96c4c9585c32bf6a75f62d9/raw/e3c6895ce42069f0ee7e991229064f167fe8ccdc/quotes.json")
      .then(res => res.json())
      .then(data => {
        // console.log(data);
        this.setState({
          quotes: data.quotes
        });
      });
    // console.log(this.state.quotes);
  }
  randomQuoteHandler = () => {
    const randNumb = Math.floor(Math.random() * this.state.quotes.length);
    const randomQuote = this.state.quotes[randNumb];
    this.setState({
      quotes: randomQuote
    });
    console.log(this.state.quotes);
  };
  render() {
    return (
      <div>
        <button onClick={this.randomQuoteHandler}>gen</button>
        <p>{this.state.quotes !== null && this.state.quotes.quote}</p>
        <p> {this.state.quotes !== null && this.state.quotes.author}</p>
      </div>
    );
  }
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

Answer 1

The randomQuoteHandler replaces this.state.quotes array with a chosen quote which is an object. So on the second click, this.state.quotes.length is undefined.

You need to store the chosen quote in another state variable like randomQuote.

class App extends React.Component {
  state = {
    quotes: null,
    randomQuote: null,
  }
  componentDidMount() {
    fetch(
      'https://gist.githubusercontent.com/camperbot/5a022b72e96c4c9585c32bf6a75f62d9/raw/e3c6895ce42069f0ee7e991229064f167fe8ccdc/quotes.json',
    )
      .then(res => res.json())
      .then(data => {
        // console.log(data);
        this.setState({
          quotes: data.quotes,
        })
      })
    // console.log(this.state.quotes);
  }
  randomQuoteHandler = () => {
    const randNumb = Math.floor(Math.random() * this.state.quotes.length)
    const randomQuote = this.state.quotes[randNumb]
    this.setState({
      randomQuote: randomQuote,
    })
    console.log(this.state.quotes)
  }
  render() {
    return (
      <div>
        <button onClick={this.randomQuoteHandler}>gen</button>
        <p>{this.state.randomQuote !== null && this.state.randomQuote.quote}</p>
        <p>{this.state.randomQuote !== null && this.state.randomQuote.author}</p>
      </div>
    )
  }
}

Answer 2

The problem is that in the randomQuoteHandler you are replacing the whole array of quotes with the random randomQuote object. The log at the end of this randomQuoteHandler function is showing that.

this.setState({
  quotes: randomQuote  // Array get replaced by one object
});

therefore the second time there is no array in the sate to read this.state.quotes.quote