Randomg things.

web/modules/custom/dc_tests/js/testing.js

@@ -0,0 +1,10 @@
+((Drupal, once) => {
+  Drupal.behaviors.myBehavior = {
+    attach(context) {
+      let target = once('myBehavior', 'body');
+      target.forEach((t) => {
+        alert('Behavior attached test');
+      });
+    },
+  };
+})(Drupal, once);