Set Twig variable with javascript/jquery for displaying entries based on clicked value I have a filter system on my website which uses categories. The categories have all got their own ID tagged to their HTML Element. Now I just need to get the clicked checkboxes to add their ID to the Twig variable which displays the entries in the for loop.

{% set categories = craft.categories.section('retrospect') %}

{% set relatedCategories = [] %}

{% for category in categories %}
  {% set relatedCategories = relatedCategories|merge([taggedIds]) %}
{% endfor %}

{% set related = craft.categories.section('retrospect').id(relatedCategories) %}

{% set relatedArticles = craft.entries.section('retrospect').relatedTo(related) %}

{% for entry in relatedArticles.order('caseNumber asc').after('2016-01').before('2016-12') %}
  {{ entry.title }}
{% endfor %}
The Twig code to fetch entries occurs on page load - Your JS code will run after the page loads and won't be able to update/fetch new entries. Instead, you should look at building a system that uses query strings to add the id's to the Twig variable on page load - then enhance this using AJAX.