примечание

app.get('/api/posts', (req, res) => {
  const pageCount = Math.ceil(posts.length / 10);
  let page = parseInt(req.query.p);
  if (!page) { page = 1;}
  if (page > pageCount) {
    page = pageCount
  }
  res.json({
    "page": page,
    "pageCount": pageCount,
    "posts": posts.slice(page * 10 - 10, page * 10)
  });
});
Fantastic Flamingo