Eleventy nunjucks useful stuff

11ty_nunjucks.njk

{% if not page.fileSlug|length %}
    This is the home page<br>
    We know this as the homepage has no slug<br>
    So when we use a filter to get the length of the page slug it returns false if we are on the homepage<br>
    So if we preceed that test with an if not conditional we know we are on the homepage<br>
    We are essentially saying if the page slug is empty do something.
    Also see it used in a ternary style arrangment below. 
{% endif %}

{{ title if page.fileSlug|length else heading }}

Use 11ty provided data to create a slug and title

{% set slug = page.fileSlug %}
{% if not slug|length %}
    {% set title = "Home" %}
{% else %}
    {% set title = slug|capitalize %}
{% endif %}

Create an empty array

{% set featured = [] %}

Get the number of items in an array

{% collections.posts | length %}

Get first or last items in an array

{% set firstPost = collections.posts | first %}
{% set lastPost = collections.posts | last %}

Use the 11ty universal filters to fetch the previous and next items in a collection

{% set previousPost = collections.posts | getPreviousCollectionItem(page) %}
{% set nextPost = collections.posts | getNextCollectionItem(page) %}

Push posts into an array

{% set featured = (featured.push(previousPost), featured) %}
{% set featured = (featured.push(nextPost), featured) %}

Check to see if an array is not empty

{% if featured | length %}
    {# Do stuff #}
{% endif %}

Show only the first n items from an array

{%- for item in collections.posts.slice(0, 2) -%}
    {# item #}
{%- endfor -%}

OTHER ELEVENTY PROVIDED DATA VARIABLES

{{ page.templateContent }}
{{ page.template }}
{{ page.url }} URL can be used in <a href> to link to other templates
{{ page.fileSlug }} For permalinks: inputPath filename minus template file extension
{{ page.filePathStem }} For permalinks: inputPath minus template file extension
{{ page.date }} JS Date Object for current page (used to sort collections)
{{ page.inputPath }} The path to the original source file for the template. Note: this will include your input directory path!
{{ page.outputPath }} Depends on your output directory (the default is _site)