react.dev/tips/12-initial-ajax.md

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initial-ajax	Load Initial Data via AJAX	tips	initial-ajax.html	dom-event-listeners.html	false-in-jsx.html

Fetch data in componentDidMount. When the response arrives, store the data in state, triggering a render to update your UI.

When processing the response of an asynchronous request, be sure to check that the component is still mounted before updating its state by using this.isMounted().

This example fetches the desired Github user's latest gist:

/** @jsx React.DOM */

var UserGist = React.createClass({
  getInitialState: function() {
    return {
      username: '',
      lastGistUrl: ''
    };
  },

  componentDidMount: function() {
    $.get(this.props.source, function(result) {
      var lastGist = result[0];
      if (this.isMounted()) {
        this.setState({
          username: lastGist.owner.login,
          lastGistUrl: lastGist.html_url
        });
      }
    }.bind(this));
  },

  render: function() {
    return (
      <div>
        {this.state.username}'s last gist is
        <a href={this.state.lastGistUrl}>here</a>.
      </div>
    );
  }
});

React.renderComponent(
  <UserGist source="https://api.github.com/users/octocat/gists" />,
  mountNode
);