carbon-components-svelte/docs/src/routes/blog/[slug].json.js

import posts from "./_posts.js";

const lookup = new Map();

posts.forEach((post) => {
  lookup.set(post.slug, JSON.stringify(post));
});

export function get(req, res, next) {
  // the `slug` parameter is available because
  // this file is called [slug].json.js
  const { slug } = req.params;

  if (lookup.has(slug)) {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(lookup.get(slug));
  } else {
    res.writeHead(404, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ message: `Not found` }));
  }
}