Initial attempt @ submenu implementation.

src/components/dropdownMenu/DropdownMenu.tsx

@@ -24,10 +24,11 @@ const DropdownMenu = ({
 }) => {
   const MenuTriggerComp = getMenuTriggerComponent(children);
   const MenuContentComp = getMenuContentComponent(children);
+
   return (
     <DropdownMenuPrimitive.Root open={open}>
       {MenuTriggerComp}
-      {open && MenuContentComp}
+      {MenuContentComp}
     </DropdownMenuPrimitive.Root>
   );
 };

src/components/dropdownMenu/DropdownMenuSub.tsx

@@ -0,0 +1,26 @@
+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import {
+  getSubMenuContentComponent,
+  getSubMenuTriggerComponent,
+} from "./dropdownMenuUtils";
+import DropdownMenuSubTrigger from "./DropdownMenuSubTrigger";
+import DropdownMenuSubContent from "./DropdownMenuSubContent";
+import DropdownMenuSubItem from "./DropdownMenuSubItem";
+
+const DropdownMenuSub = ({ children }: { children?: React.ReactNode }) => {
+  const MenuTriggerComp = getSubMenuTriggerComponent(children);
+  const MenuContentComp = getSubMenuContentComponent(children);
+  return (
+    <DropdownMenuPrimitive.Sub>
+      {MenuTriggerComp}
+      {MenuContentComp}
+    </DropdownMenuPrimitive.Sub>
+  );
+};
+
+DropdownMenuSub.Trigger = DropdownMenuSubTrigger;
+DropdownMenuSub.Content = DropdownMenuSubContent;
+DropdownMenuSub.Item = DropdownMenuSubItem;
+
+export default DropdownMenuSub;
+DropdownMenuSub.displayName = "DropdownMenuSub";

src/components/dropdownMenu/DropdownMenuSubContent.tsx

@@ -0,0 +1,38 @@
+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import { useDevice } from "../App";
+import Stack from "../Stack";
+import { Island } from "../Island";
+import clsx from "clsx";
+
+const DropdownMenuSubContent = ({
+  children,
+  className,
+}: {
+  children?: React.ReactNode;
+  className?: string;
+}) => {
+  const device = useDevice();
+
+  const classNames = clsx(`dropdown-menu ${className}`, {
+    "dropdown-menu--mobile": device.isMobile,
+  }).trim();
+
+  return (
+    <DropdownMenuPrimitive.SubContent className={classNames}>
+      {device.isMobile ? (
+        <Stack.Col className="dropdown-menu-container">{children}</Stack.Col>
+      ) : (
+        <Island
+          className="dropdown-menu-container"
+          padding={2}
+          style={{ zIndex: 1 }}
+        >
+          {children}
+        </Island>
+      )}
+    </DropdownMenuPrimitive.SubContent>
+  );
+};
+
+export default DropdownMenuSubContent;
+DropdownMenuSubContent.displayName = "DropdownMenuSubContent";

src/components/dropdownMenu/DropdownMenuSubItem.tsx

@@ -0,0 +1,39 @@
+import MenuItemContent from "./DropdownMenuItemContent";
+import {
+  getDropdownMenuItemClassName,
+  useHandleDropdownMenuItemClick,
+} from "./common";
+
+const DropdownMenuSubItem = ({
+  icon,
+  onSelect,
+  children,
+  shortcut,
+  className,
+  ...rest
+}: {
+  icon?: JSX.Element;
+  onSelect: (event: Event) => void;
+  children: React.ReactNode;
+  shortcut?: string;
+  className?: string;
+} & Omit<React.ButtonHTMLAttributes<HTMLButtonElement>, "onSelect">) => {
+  const handleClick = useHandleDropdownMenuItemClick(rest.onClick, onSelect);
+
+  return (
+    <button
+      {...rest}
+      onClick={handleClick}
+      type="button"
+      className={getDropdownMenuItemClassName(className)}
+      title={rest.title ?? rest["aria-label"]}
+    >
+      <MenuItemContent icon={icon} shortcut={shortcut}>
+        {children}
+      </MenuItemContent>
+    </button>
+  );
+};
+
+export default DropdownMenuSubItem;
+DropdownMenuSubItem.displayName = "DropdownMenuSubItem";

src/components/dropdownMenu/DropdownMenuSubTrigger.tsx

@@ -0,0 +1,29 @@
+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import React from "react";
+import MenuItemContent from "./DropdownMenuItemContent";
+import { getDropdownMenuItemClassName } from "./common";
+
+const DropdownMenuSubTrigger = ({
+  children,
+  icon,
+  shortcut,
+  className,
+}: {
+  children: React.ReactNode;
+  icon?: JSX.Element;
+  shortcut?: string;
+  className?: string;
+}) => {
+  return (
+    <DropdownMenuPrimitive.SubTrigger
+      className={getDropdownMenuItemClassName(className)}
+    >
+      <MenuItemContent icon={icon} shortcut={shortcut}>
+        {children}
+      </MenuItemContent>
+    </DropdownMenuPrimitive.SubTrigger>
+  );
+};
+
+export default DropdownMenuSubTrigger;
+DropdownMenuSubTrigger.displayName = "DropdownMenuSubTrigger";

src/components/dropdownMenu/dropdownMenuUtils.ts

@@ -1,6 +1,6 @@
 import React from "react";
 
-export const getMenuTriggerComponent = (children: React.ReactNode) => {
+const getMenuComponent = (component: string) => (children: React.ReactNode) => {
   const comp = React.Children.toArray(children).find(
     (child) =>
       React.isValidElement(child) &&
@@ -8,7 +8,7 @@ export const getMenuTriggerComponent = (children: React.ReactNode) => {
       //@ts-ignore
       child?.type.displayName &&
       //@ts-ignore
-      child.type.displayName === "DropdownMenuTrigger",
+      child.type.displayName === component,
   );
   if (!comp) {
     return null;
@@ -17,19 +17,11 @@ export const getMenuTriggerComponent = (children: React.ReactNode) => {
   return comp;
 };
 
-export const getMenuContentComponent = (children: React.ReactNode) => {
-  const comp = React.Children.toArray(children).find(
-    (child) =>
-      React.isValidElement(child) &&
-      typeof child.type !== "string" &&
-      //@ts-ignore
-      child?.type.displayName &&
-      //@ts-ignore
-      child.type.displayName === "DropdownMenuContent",
-  );
-  if (!comp) {
-    return null;
-  }
-  //@ts-ignore
-  return comp;
-};
+export const getMenuTriggerComponent = getMenuComponent("DropdownMenuTrigger");
+export const getMenuContentComponent = getMenuComponent("DropdownMenuContent");
+export const getSubMenuTriggerComponent = getMenuComponent(
+  "DropdownMenuSubTrigger",
+);
+export const getSubMenuContentComponent = getMenuComponent(
+  "DropdownMenuSubContent",
+);

src/components/main-menu/MainMenu.tsx

@@ -14,6 +14,7 @@ import { HamburgerMenuIcon } from "../icons";
 import { withInternalFallback } from "../hoc/withInternalFallback";
 import { composeEventHandlers } from "../../utils";
 import { useTunnels } from "../context/tunnels";
+import DropdownMenuSub from "../dropdownMenu/DropdownMenuSub";
 
 const MainMenu = Object.assign(
   withInternalFallback(
@@ -77,6 +78,7 @@ const MainMenu = Object.assign(
     ItemCustom: DropdownMenu.ItemCustom,
     Group: DropdownMenu.Group,
     Separator: DropdownMenu.Separator,
+    Sub: DropdownMenuSub,
     DefaultItems,
   },
 );

src/packages/excalidraw/example/App.tsx

@@ -506,6 +506,16 @@ export default function App({ appTitle, useCustom, customArgs }: AppProps) {
   const renderMenu = () => {
     return (
       <MainMenu>
+        <MainMenu.Sub>
+          <MainMenu.Sub.Trigger>Trigger</MainMenu.Sub.Trigger>
+          <MainMenu.Sub.Content>
+            <MainMenu.Sub.Item
+              onSelect={() => window.alert("You clicked on sub item")}
+            >
+              Sub item
+            </MainMenu.Sub.Item>
+          </MainMenu.Sub.Content>
+        </MainMenu.Sub>
         <MainMenu.DefaultItems.SaveAsImage />
         <MainMenu.DefaultItems.Export />
         <MainMenu.Separator />