fix: ensure renderOne re-runs update on every call without data

Using a shared null reference caused renderList's identity check to skip
the update callback on subsequent renderOne calls. Pass a fresh object
each time so the update always runs.

Author: psd-coder

packages/nanotags/package.json

@@ -82,7 +82,7 @@
     },
     {
       "path": ".size-check/render.mjs",
-      "limit": "410 B"
+      "limit": "417 B"
     },
     {
       "path": ".size-check/context.mjs",

packages/nanotags/src/render.test.ts

@@ -220,6 +220,54 @@ describe("render", () => {
     expect(container.children[0]).toBe(firstEl);
   });
 
+  it("re-runs update callback without data on subsequent calls", () => {
+    const container = createHostWith("");
+    const tpl = makeTpl("<span></span>");
+    let callCount = 0;
+
+    const update = (el: Element) => {
+      callCount++;
+      el.textContent = `call-${callCount}`;
+    };
+
+    render(container, tpl, { update });
+    expect(callCount).toBe(1);
+    expect(container.children[0]?.textContent).toBe("call-1");
+
+    render(container, tpl, { update });
+    expect(callCount).toBe(2);
+    expect(container.children[0]?.textContent).toBe("call-2");
+
+    render(container, tpl, { update });
+    expect(callCount).toBe(3);
+    expect(container.children[0]?.textContent).toBe("call-3");
+  });
+
+  it("skips update when explicit data has not changed", () => {
+    const container = createHostWith("");
+    const tpl = makeTpl("<span></span>");
+    let callCount = 0;
+    const data = { name: "Alice" };
+
+    render(container, tpl, {
+      data,
+      update: (el, d) => {
+        callCount++;
+        el.textContent = d.name;
+      },
+    });
+    expect(callCount).toBe(1);
+
+    render(container, tpl, {
+      data,
+      update: (el, d) => {
+        callCount++;
+        el.textContent = d.name;
+      },
+    });
+    expect(callCount).toBe(1);
+  });
+
   it("switches between different templates", () => {
     const container = createHostWith("");
     const loadingTpl = makeTpl('<div class="loading">Loading...</div>');

packages/nanotags/src/render.ts

@@ -87,8 +87,11 @@ export function render<T, E extends Element = Element>(
   template: HTMLTemplateElement,
   options?: RenderOptions<T, E>,
 ): void {
+  // When no explicit data is provided, use a fresh object each call
+  // so renderList's identity check always passes and update always runs
+  const data = [options !== undefined && "data" in options ? options.data : {}] as T[];
   renderList(container, template, {
-    data: [options?.data ?? (null as T)],
+    data,
     key: () => {
       let id = tplIds.get(template);
       if (id === undefined) {