Implementing Link Header Pagination on the Node.js Server

In the past few years, more and more APIs have begun to follow the RFC5988 convention of using the Link header to provide URLs for the next page. We can do this too and it’s quite easy.

Here is a function I recently wrote to do this for the simple case of a big array:

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function paginate(sourceList, page, perPage) {
  var totalCount = sourceList.length;
  var lastPage = Math.floor(totalCount / perPage);
  var sliceBegin = page*perPage;
  var sliceEnd = sliceBegin+perPage;
  var pageList = sourceList.slice(sliceBegin, sliceEnd);
  return {
    pageData: pageList,
    nextPage: page < lastPage ? page+1 : null,
    totalCount: totalCount
  }
}

To demonstrate the usage, imagine you have defined a function getMovies which provides a movieList array you wish to paginate.
You have an express route /movies which serves as the web API to your movie library.
You might create a paginated route like this:

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app.get('/movies', function(req, res) {
  var pageNum = parseInt(req.query.page || 0);
  var perPage = parseInt(req.query.per_page || 50);
  getMovies(function(err, movieList) {
    if (err) throw err;
    var page = paginate(movieList, pageNum, perPage);
    if (page.nextPage) {
      res.set("Link", "/movies?page="+page.nextPage);
    }
    res.set("X-Total-Count", movieList.length);
    res.json(page.pageData);
  });
})

Note that in most cases, you would not be paginating from a big array. This was my first time paginating a fairly large set which was not from a database. In the case of database access, your function won’t be so general since it will depend on using the database API to create an efficient query by offset and limit.