fix: fetcher.submit failing with plain objects containing tagName pro…

.changeset/fluffy-walls-add.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Fix `fetcher.submit` failing with plain objects containing a `tagName` property

packages/react-router/__tests__/dom/fetcher-submit-tagname-test.tsx

@@ -0,0 +1,98 @@
+import * as React from "react";
+import { render, fireEvent, screen } from "@testing-library/react";
+import "@testing-library/jest-dom";
+import {
+  RouterProvider,
+  createBrowserRouter,
+  useFetcher,
+} from "../../index";
+import getWindow from "../utils/getWindow";
+
+describe("fetcher.submit with tagName property", () => {
+  it("should handle plain object with tagName property", async () => {
+    let actionSpy = jest.fn();
+    actionSpy.mockReturnValue({ ok: true });
+
+    let router = createBrowserRouter(
+      [
+        {
+          path: "/",
+          action: actionSpy,
+          Component() {
+            let fetcher = useFetcher();
+            return (
+              <button
+                onClick={() =>
+                  fetcher.submit(
+                    { tagName: "div", data: "test" },
+                    { method: "post" }
+                  )
+                }
+              >
+                Submit
+              </button>
+            );
+          },
+        },
+      ],
+      {
+        window: getWindow("/"),
+      }
+    );
+
+    render(<RouterProvider router={router} />);
+    fireEvent.click(screen.getByText("Submit"));
+
+    expect(actionSpy).toHaveBeenCalled();
+    let formData = await actionSpy.mock.calls[0][0].request.formData();
+    expect(formData.get("tagName")).toBe("div");
+    expect(formData.get("data")).toBe("test");
+  });
+
+  it("should handle plain object with various HTML element-like properties", async () => {
+    let actionSpy = jest.fn();
+    actionSpy.mockReturnValue({ ok: true });
+
+    let router = createBrowserRouter(
+      [
+        {
+          path: "/",
+          action: actionSpy,
+          Component() {
+            let fetcher = useFetcher();
+            return (
+              <button
+                onClick={() =>
+                  fetcher.submit(
+                    {
+                      tagName: "button",
+                      className: "test-class",
+                      id: "test-id",
+                      value: "test-value",
+                    },
+                    { method: "post" }
+                  )
+                }
+              >
+                Submit
+              </button>
+            );
+          },
+        },
+      ],
+      {
+        window: getWindow("/"),
+      }
+    );
+
+    render(<RouterProvider router={router} />);
+    fireEvent.click(screen.getByText("Submit"));
+
+    expect(actionSpy).toHaveBeenCalled();
+    let formData = await actionSpy.mock.calls[0][0].request.formData();
+    expect(formData.get("tagName")).toBe("button");
+    expect(formData.get("className")).toBe("test-class");
+    expect(formData.get("id")).toBe("test-id");
+    expect(formData.get("value")).toBe("test-value");
+  });
+});

packages/react-router/lib/dom/dom.ts

@@ -7,7 +7,9 @@ export const defaultMethod: HTMLFormMethod = "get";
 const defaultEncType: FormEncType = "application/x-www-form-urlencoded";
 
 export function isHtmlElement(object: any): object is HTMLElement {
-  return object != null && typeof object.tagName === "string";
+  return (
+    typeof HTMLElement !== "undefined" && object instanceof HTMLElement
+  );
 }
 
 export function isButtonElement(object: any): object is HTMLButtonElement {