why is react a js library code example

Example: use javascript library in react

class MainView extends Component {
  render() {
    // don't render anything
    return 
;
  },

  componentDidMount() {
    // find the DOM node for this component
    const node = ReactDOM.findDOMNode(this);

    // widget does stuff
    $(node).activateMyCoolWidget();

    // start a new React render tree with widget node
    ReactDOM.render(
{this.props.children}
, node);
  }
});