Giulia Chiola

Posted on Jan 20, 2021 • Edited on Aug 22, 2022 • Originally published at giuliachiola.dev

Add items to an array in Nunjucks

#nunjucks #twig

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: 📒 Nunjuks scoped variable declarations

📚 More info

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

Top comments (12)

Felipe Andrade • Apr 26 '23 • Edited

Instead of push use concat, it will simplify things a bit:

{% set domesticAnimals = domesticAnimals.concat(animal) %}

Giulia Chiola • May 19 '23

Thanks for sharing Felipe! I didn't know about the concact() method. I've just checked the official Mozilla blog, and they wrote only about join() for concatenate string. Thanks for make me discovering it!

Pavel Yefimov • Feb 7 '23

Thanx for inspiration!

I've ended up with the following:

{%- set slides = [1, 2] %}
{{- slides.push(3) | reject() }}
{{ slides | dump }}

Result in output:

[1, 2, 3]

Giulia Chiola • May 19 '23

I din't know the reject() method! Thanks for sharing Pavel!

Vadim Makeev • Jul 10 '22

Thank you! I had no idea that you can execute arbitrary JS right in the tags.

Do you know where I can read more about that? You’re not just reassigning the value with the pushed item, it’s also wrapped in brackets and you repeat array’s name after a comma. Where this comes from? 🤔

Giulia Chiola • Aug 22 '22

hey Vadim, thank you for your feedback! I just added at the end of the post where I found the push syntax 😊 I can't really tell why this filter is not available on the official docs.

BDhara • Feb 3 '22 • Edited

It is a great post. though I am stuck at a point where I need to pass this final array to another statement such as: window.master.init({{domesticAnimals}});. this shows window.master.init(cat,dog); instead of array. what should I do to pass an array in the above statement. I need data like `window.master.init(['cat','dog']).