Node pagination with express

Question

I have to build and API as server side, that should provide results in pages of 10 entries, using only Node with express (no other packages).

• A query parameter p specifies which page to return, starting with 1. If the p parameter is omitted, the default value is 1.

• If the client side asks for /api/stories?p=1, they should only get 10 stories, starting from the newest one.

• If p=2, the API must return the second batch of 10 stories. When a page of stories is returned it must be ordered with the most recent story first.

• If p is greater than the last page number, the API must return the last available page.

• The page value is the currently returned page. If the requested page p is greater than the last page number, the returned page value will indicate the last page number.

• The pageCount value is the number of the last non-empty page.*

This is what I have for pagination...

//pagination
const pageLimit = 10;
app.get('/api/posts', function(req, res) {
  res.json({
    "posts": posts.slice(-pageLimit).reverse(),
    "page": 1,
    "pageCount": Math.ceil(posts.length / 10)
  });
});

The return is correct as 10 posts per page, 11th, 21st, 31st posts are pushed on 2nd ,3rd page etc... Now my problem comes when I try to advance from page 1 to page 2 (as a next page) nothing happens...

I'm guessing I have to implement something like a a next but I don't have any idea how to do it

Any help would be appreciated...

Answer 1

after scratching my head 2 days, I found a solution that works for me..Thank you num8er for pointing me in right direction...

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)
  });
});

Answer 2

Check this out:

app.get('/api/posts', (req, res) => {
  const postCount = posts.length;
  const perPage = 10;
  const pageCount = Math.ceil(postCount / perPage);

  let page = parseInt(req.query.p);
  if(page < 1) page = 1;
  if(page > pageCount) page = pageCount;

  const from = postCount - ((page - 1) * perPage) - 1; // ex.: 44 - ((1 - 1) * 10) -1 = 43 (44 is count, 43 is index)
  let to = postCount - (page * perPage); // ex.: 44 - (1 * 10) = 34
  if(to < 0) to = 0;

  res.json({
    posts: posts.slice(from, to).reverse(),
    page,
    pageCount
  });
});

P.S. If posts array retrieved from database - I strongly recommend to use database powers to retrieve necessary data. Otherwise retrieving thousands of page and then slicing array to 10 items is will result with performance issues.