const PostList = ({posts}) => ( posts.map(post => ) ) class PostPage extends Component { state = { posts: [], category: "" } componentDidMount() { fetchPost().then(posts => this.setState({posts})) } render() { const { category } = this.state; const posts = this.state.posts.filter(post => post.category === category) return <> this.setState({category: e.target.value})} value={category} /> } }