How to access page variable in pagination before filter

[joshwalsh]

I have a collections.postsByCategory which takes my collections.posts and returns a 2 dimensional array of those posts grouped by the fileSlug of the associated category.

This works great to build a category page that loops through all the posts in that category, but I'm struggling to figure out how to paginate this collection since it depends on passing in the fileSlug of the current loaded page (the category).

Specifically, I'm trying to use a before in order to return just the subset of the array I need, but this fails because I don't have access to the page variable in the scope of that before in order to get the current pages fileSlug.

Am I going about this wrong?

---js
{
  layout: "default",
  pagination: {
    data: "collections.postsByCategory",
    size: 10,
    alias: "posts",
    before: function(data) {
      return data[page.fileSlug];
      }
  }
}
---