Is there a way to use 'eleventyExcludeFromCollections' in the eleventyComputed property?

[mark-reason]

I'm trying to use page data to decide whether a page is excluded from collections, something like this:

---js
{
  layout: "layouts/base.html",
  pagination: {
    data: "pages",
    alias: "pg",
    size: 1,
    addAllPagesToCollections: true,
  },
  eleventyComputed: {
    title: (data) => data.pg.title,
    eleventyExcludeFromCollections: (data) => {
      return data.pg.permalink === '/excluded-page';
    },
  }
}
---

However this seems to always return 'true' even if it's not. Even if I just 'return false' then all pages are then excluded from collections.

[pdehaan]

I would have expected your solution to work, but I'm struggling to figure out locally why it isnt working for me.
My quick workaround was to create a custom collection based on a tag and just re-filter the collection based on eleventyExcludeFromCollections frontmatter.

// .eleventy.js snippet
    eleventyConfig.addCollection("pages", function (collectionApi) {
        const pages = [...collectionApi.getFilteredByTag("pages")];
        return pages.filter(p => {
            return !p.data.eleventyExcludeFromCollections;
        });
    });

---
# src/pagination.njk
pagination:
    data: "pages"
    alias: "pg"
    size: 1
    addAllPagesToCollections: true
permalink: "{{ pg.permalink }}"
tags:
    - pages
---

<h1>title={{ title }}</h1>
<p>permalink={{ pg.permalink }}</p>
<p>eleventyExcludeFromCollections={{ eleventyExcludeFromCollections }}</p>
<p>draft={{ pg.draft }}</p>
<p>{{ page | inspect }}</p>

// src/pagination.11tydata.js (because I find it easier than JSON front matter. 🤷 )
module.exports = () => {
  return {
    eleventyComputed: {
      title(data) {
        return data.pg.title;
      },
      eleventyExcludeFromCollections(data) {
        if (data.pg.draft || data.page.url === "/excluded-page/") {
            return true;
        }
        return false;
      },
    },
  };
};

src/_data/pages.json

[
    {"title": "Page 1", "permalink": "/page-number-one/" },
    {"title": "Page two", "permalink": "/nested/page/two/", "draft": true},
    {"title": "secret page", "permalink": "/excluded-page/"}
]

---
# src/collection-test.njk
---
{% for p in collections.pages %}
<p>{{ p.data.title }} {{ p.url }} {{ p.data.draft | inspect }}</p>
{% endfor %}

OUTPUT

<p>Page 1 /page-number-one/ undefined</p>

Note that "Page 2" isn't listed (because we set custom draft: true flag) and "secret page" isn't listed (because it's generated url/permalink matches that disallow list).

[darekkay]

I would have expected your solution to work, but I'm struggling to figure out locally why it isnt working for me.

I think this note on the Computed Data page provides the answer:

It is important to note that Computed Data is computed right before templates are rendered. Therefore Computed Data cannot be used to modify the special data properties used to configure templates (e.g. layout, pagination, tags etc.). These restrictions may be relaxed over time.