Troubleshooting code to display post titles in a specific category, with discussion on iterating over posts and handling non-existent categories.

export const loader: LoaderFunction = async ({ params }) => {
  const categoryData = await getClient().fetch(
    `*[_type == "category" && slug.current == $slug]{ 
      _id, 
      title, 
      slug,
      description,
      "posts": *[_type == 'post' && references(^._id)]{title}
    } | order(publishedAt desc) `,
    { slug: params.slug }
  );

  return { categoryData };
};

export default function Category() {
  let { categoryData } = useLoaderData();

  return (
    <div>
      <div>{categoryData[0].title}</div>
      <div>{categoryData[0].posts.title}</div>
    </div>
  );
}

name: "category",
  title: "Category",
  type: "document",
  fields: [
    {
      name: "title",
      title: "Title",
      type: "string",
    },
    {
      name: "slug",
      type: "slug",
      title: "Slug",
      options: {
        source: "title",
      },
    },
    {
      name: "description",
      title: "Description",
      type: "text",
    },
  ],
};

param $slug referenced, but not provided
*[_type == "category" && slug.current == $slug]{ 
-----------------------------------------^^^^
Line:   0
Column: 41

*[_type == "category" && slug.current == $slug]{ 
			_id, 
			title, 
			slug,
			description,
			"posts": *[_type == 'post' && references(^._id)]{title},
		}

{categoryData[0].posts.map(p => p.title)}