Fix menu dropdown focus traps (#944)

bookmarks/frontend/behaviors/dropdown.js

@@ -6,23 +6,38 @@ class DropdownBehavior extends Behavior {
     this.opened = false;
     this.onClick = this.onClick.bind(this);
     this.onOutsideClick = this.onOutsideClick.bind(this);
+    this.onEscape = this.onEscape.bind(this);
+    this.onFocusOut = this.onFocusOut.bind(this);
+
+    // Prevent opening the dropdown automatically on focus, so that it only
+    // opens on click then JS is enabled
+    this.element.style.setProperty("--dropdown-focus-display", "none");
+    this.element.addEventListener("keydown", this.onEscape);
+    this.element.addEventListener("focusout", this.onFocusOut);
 
     this.toggle = element.querySelector(".dropdown-toggle");
+    this.toggle.setAttribute("aria-expanded", "false");
     this.toggle.addEventListener("click", this.onClick);
   }
 
   destroy() {
     this.close();
     this.toggle.removeEventListener("click", this.onClick);
+    this.element.removeEventListener("keydown", this.onEscape);
+    this.element.removeEventListener("focusout", this.onFocusOut);
   }
 
   open() {
+    this.opened = true;
     this.element.classList.add("active");
+    this.toggle.setAttribute("aria-expanded", "true");
     document.addEventListener("click", this.onOutsideClick);
   }
 
   close() {
+    this.opened = false;
     this.element.classList.remove("active");
+    this.toggle.setAttribute("aria-expanded", "false");
     document.removeEventListener("click", this.onOutsideClick);
   }
 
@@ -39,6 +54,20 @@ class DropdownBehavior extends Behavior {
       this.close();
     }
   }
+
+  onEscape(event) {
+    if (event.key === "Escape" && this.opened) {
+      event.preventDefault();
+      this.close();
+      this.toggle.focus();
+    }
+  }
+
+  onFocusOut(event) {
+    if (!this.element.contains(event.relatedTarget)) {
+      this.close();
+    }
+  }
 }
 
 registerBehavior("ld-dropdown", DropdownBehavior);