Add items to an array in Nunjucks

To add items in Nunjucks, use the .push() function.

{% set arr = [1,2] %}
{% set arr = (arr.push(3), arr) %}

Final array:

arr = [1,2,3]

Unfortunately, I did not found any references in the official Nunjucks documentation for this useful function 🤷🏻‍♀️

{% set animals = ['cat 🐱', 'dog 🐶', 'lion 🦁'] %}
{% set domesticAnimals = [] %}
{% for animal in animals %}
  {% if animal !== 'lion' %}
    {% set domesticAnimals = (domesticAnimals.push(animal), domesticAnimals) %}
  {% endif %}
{% endfor %}

Final array:

domesticAnimals = ['cat 🐱', 'dog 🐶']

🧨 !important

If you use {% set .... %} inside a for-loop block, pay attention to have defined it outside before entering the loop.
I wrote a post about it: 📒 Nunjucks scoped variable declarations

📚 More info

Docs about Twig 'push' filter. Note that this filter is not present into the official Twig documentation 🤷🏻‍♀️