I'm learning Eleventy. Coming from writing (mostly) strictly typed code, JS is really frustrating. It's possibly because I'm using VS Code instead of Intellij, but I don't know how method or type hinting could work. I'll try it out at some point.

I figured out a basic method to sort Eleventy collections;

// Sort with `Array.sort`
eleventyConfig.addCollection("sortedNav", function(collection) {
    return collection.getFilteredByTag("nav").sort(function(a, b) {
        return a.data.priority - b.data.priority;
    });
});

I'm using this to sort the nav collection, which is the main navigation at the top of the page. You simply add a frontmatter item named priority;

title: Some Page
tags:
- nav
priority: 1

Finally, you need to switch whatever code is loading the nav collection to use the new sortedNav collection instead;

<ul class="nav page-header__nav">
    {%- for nav in collections.sortedNav -%}
    <li class="nav-item{% if nav.url == page.url %} nav-item-active{% endif %}"><a href="{{ nav.url | url }}">{{ nav.data.navtitle }}</a></li>
    {%- endfor -%}
</ul>