loading.js

function DisplayPosts({posts}) {
  return (
    <ul>
      { posts.map(({id, text}) => (<li key={id}>{text}</li>)) }
    </ul>
  );
}

function loaderHoc(Component) {
  return class LoaderComponent extends React.Component {
    constructor(props) {
      super(props);
      this.state = {
        loaded: false,
        data: {}
      };
      
      fetch(props.url).then(_ => this.setState({ loaded: true, data: _ }));
    }
    
    render() {
      const { url, propsExceptUrl } = this.props;
      const { loaded, data } = this.state;
      return (loaded ? "Loading..." : <Component {...propsExceptUrl} {...data} />);
    }
  }
}

const LoaderDisplay = loaderHoc(DisplayPosts);

<LoaderDisplay url="..." />