A component is one JS class. Do you want to include another component in your component? Just import it:

import {ProductDetail} from "./ProductDetail";

interface Props {
    products: Product[];
}
export class ProductList extends React.Component<Props, undefined> {
    render() {
        return <div>
            {this.props.products.map(th => <ProductDetail key={th.id} product={th} />)}
        </div>
    }
}