AJAX and APIs

You can use any AJAX library you like with React. Some popular ones are axios and the browser built-in fetch.

You should populate data with AJAX calls in the componentDidMount lifecycle method. This is so you can use setState to update your component when the data is retrieved.

Using AJAX Results to Set Local State

The component below demonstrates how to make an AJAX call in componentDidMount to populate local component state.

The example API returns a JSON object like this:

{
  items: [
    { id: 1, name: 'Apples', price: '$2' },
    { id: 2, name: 'Peaches', price: '$5' }
  ] 
}

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      error: null,
      isLoaded: false,
      items: []
    };
  }

  componentDidMount() {
    fetch("https://api.example.com/items")
      .then(res => res.json())
      .then(
        (result) => {
          this.setState({
            isLoaded: true,
            items: result.items
          });
        },
        // Note: it's important to handle errors here
        // instead of a catch() block so that we don't swallow
        // exceptions from actual bugs in components.
        (error) => {
          this.setState({
            isLoaded: true,
            error
          });
        }
      )
  }

  render() {
    const { error, isLoaded, items } = this.state;
    if (error) {
      return <div>Error: {error.message}</div>;
    } else if (!isLoaded) {
      return <div>Loading...</div>;
    } else {
      return (
        <ul>
          {items.map(item => (
            <li key={item.name}>
              {item.name} {item.price}
            </li>
          ))}
        </ul>
      );
    }
  }
}

Cancellation

Note that if the component unmounts before an AJAX call is complete, you may see a warning like cannot read property 'setState' of undefined. If this is an issue you may want to keep track of inflight AJAX requests and cancel them in the componentWillUnmount lifecycle method.