Issue #3384272: Allow to validate Apache/Nginx configuration requirement for aggregation folder before enabling aggregation.

core/modules/system/js/assets.validate.js

+((Drupal, once) => {
+  Drupal.behaviors.systemPerformanceAssetsValidate = {
+    attach: (context, settings) => {
+      const getAssetsValidationMessenger = () => {
+        return new Drupal.Message(
+          context.querySelector('[data-assets-validate-messages]'),
+        );
+      };
+      const validate = (e) => {
+        const el = e.currentTarget;
+        if (!el.checked) {
+          return;
+        }
+        const validateUrl = el.dataset.performanceAssetsValidatePath;
+        getAssetsValidationMessenger().clear();
+        try {
+          fetch(validateUrl)
+            .then((response) => {
+              if (response.status === 404) {
+                getAssetsValidationMessenger().add(
+                  Drupal.t(
+                    'Your server is not configured properly to access @name assets. Review Drupal server requirements.',
+                    {
+                      '@name': el.name,
+                    },
+                  ),
+                  {
+                    type: 'error',
+                  },
+                );
+              } else {
+                getAssetsValidationMessenger().add(
+                  Drupal.t(
+                    'Your server is configured properly to access @name assets.',
+                    {
+                      '@name': el.name,
+                    },
+                  ),
+                );
+              }
+            })
+            .catch((error) => {
+              getAssetsValidationMessenger().add(
+                Drupal.t(
+                  'Unable to check server requirements for @name assets.',
+                  {
+                    '@name': el.name,
+                  },
+                ),
+                {
+                  type: 'warning',
+                },
+              );
+            });
+        } catch (err) {
+          getAssetsValidationMessenger().add(
+            Drupal.t('Unable to check server requirements for @name assets.', {
+              '@name': el.name,
+            }),
+            {
+              type: 'warning',
+            },
+          );
+        }
+      };
+      once('performance-assets-validate', document.body).forEach(() => {
+        context
+          .querySelectorAll('[data-performance-assets-validate-path]')
+          .forEach((chb) => {
+            chb.addEventListener('change', validate);
+          });
+      });
+    },
+  };
+})(Drupal, once);