All files for deployment ready and tested - further development in this repo.

admin/js/filters.js

@@ -0,0 +1,30 @@
+/**
+ * Persist changelist filters state (collapsed/expanded).
+ */
+'use strict';
+{
+    // Init filters.
+    let filters = JSON.parse(sessionStorage.getItem('django.admin.filtersState'));
+
+    if (!filters) {
+        filters = {};
+    }
+
+    Object.entries(filters).forEach(([key, value]) => {
+        const detailElement = document.querySelector(`[data-filter-title='${CSS.escape(key)}']`);
+
+        // Check if the filter is present, it could be from other view.
+        if (detailElement) {
+            value ? detailElement.setAttribute('open', '') : detailElement.removeAttribute('open');
+        }
+    });
+
+    // Save filter state when clicks.
+    const details = document.querySelectorAll('details');
+    details.forEach(detail => {
+        detail.addEventListener('toggle', event => {
+            filters[`${event.target.dataset.filterTitle}`] = detail.open;
+            sessionStorage.setItem('django.admin.filtersState', JSON.stringify(filters));
+        });
+    });
+}