diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5739d2e..61d36a7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -42,6 +42,18 @@ jobs:
           deno fmt --check
           deno lint
 
+  TestJavaScript:
+    name: JavaScript / Test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: denoland/setup-deno@v2
+        with:
+          deno-version: v2.x
+      - run: deno install
+      - run: npx playwright install chromium
+      - run: deno task vitest --run
+
   TypecheckJavaScript:
     name: JavaScript / Typecheck
     runs-on: ubuntu-latest
diff --git a/.gitignore b/.gitignore
index 3fd821e..b210285 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,5 @@ dist/
 .venv
 examples/test.mcool
 *.bigWig
+node_modules
+__screenshots__
diff --git a/deno.json b/deno.json
index be08ec6..c609edd 100644
--- a/deno.json
+++ b/deno.json
@@ -1,5 +1,6 @@
 {
   "lock": false,
+  "nodeModulesDir": "auto",
   "compilerOptions": {
     "checkJs": true,
     "lib": ["dom", "dom.iterable", "esnext"]
@@ -11,5 +12,15 @@
   },
   "fmt": {
     "exclude": ["examples"]
+  },
+  "tasks": {
+    "vitest": "deno run -A vitest"
+  },
+  "imports": {
+    "@anywidget/types": "npm:@anywidget/types@^0.2.0",
+    "@deno/vite-plugin": "npm:@deno/vite-plugin@^1.0.6",
+    "@vitest/browser-playwright": "npm:@vitest/browser-playwright@^4.0.18",
+    "vite": "npm:vite@^7.3.1",
+    "vitest": "npm:vitest@^4.0.18"
   }
 }
diff --git a/src/higlass/types.ts b/src/higlass/types.ts
index bcb41b2..4f30c3a 100644
--- a/src/higlass/types.ts
+++ b/src/higlass/types.ts
@@ -82,5 +82,7 @@ export type GenomicLocation = {
 
 /** Partial types for the viewconf */
 export type Viewconf = {
-  views: Array<{ uid: string }>;
+  views: Array<
+    { uid: string; layout?: unknown; tracks?: unknown }
+  >;
 };
diff --git a/src/higlass/widget.js b/src/higlass/widget.js
index f46cf49..c00474a 100644
--- a/src/higlass/widget.js
+++ b/src/higlass/widget.js
@@ -1,6 +1,7 @@
 import * as hglib from "https://esm.sh/higlass@1.13?deps=react@17,react-dom@17,pixi.js@6";
 import { v4 } from "https://esm.sh/@lukeed/uuid@2.0.1";
 
+/** @import { AnyModel } from "@anywidget/types" */
 /** @import { PluginDataFetcherConstructor, GenomicLocation, Viewconf, DataFetcher} from "./types.ts" */
 
 const NAME = "jupyter";
@@ -111,7 +112,7 @@ function assert(expression, msg = "") {
  * ```
  *
  * @template T
- * @param {import("npm:@anywidget/types").AnyModel} model
+ * @param {AnyModel} model
  * @param {{ payload: unknown, signal?: AbortSignal }} options
  * @return {Promise<{ payload: T, buffers: Array<DataView> }>}
  */
@@ -192,7 +193,7 @@ function resolveJupyterServers(viewConfig) {
 }
 
 /**
- * @param {import("npm:@anywidget/types@0.2.0").AnyModel<State>} model */
+ * @param {AnyModel<State>} model */
 async function registerJupyterHiGlassDataFetcher(model) {
   if (window?.higlassDataFetchersByType?.[NAME]) {
     return;
@@ -286,7 +287,7 @@ function addEventListenersTo(el) {
  */
 
 export default {
-  /** @type {import("npm:@anywidget/types").Render<State>} */
+  /** @type {import("@anywidget/types").Render<State>} */
   async render({ model, el }) {
     await Promise.all([
       requireScripts(model.get("_plugin_urls")),
diff --git a/src/higlass/widget.test.ts b/src/higlass/widget.test.ts
new file mode 100644
index 0000000..c7934a6
--- /dev/null
+++ b/src/higlass/widget.test.ts
@@ -0,0 +1,66 @@
+import { expect, onTestFinished, test, vi } from "vitest";
+import type { AnyModel, Experimental } from "@anywidget/types";
+import type { State } from "./widget.js";
+
+const experimental: Experimental = {
+  invoke() {
+    throw new Error("experimental.invoke is not implemented.");
+  },
+};
+
+test("render creates a HiGlass viewer with a simple viewconf", async () => {
+  const { default: widget } = await import("./widget.js");
+
+  const el = document.createElement("div");
+  el.style.width = "800px";
+  el.style.height = "400px";
+  document.body.appendChild(el);
+  onTestFinished(() => el.remove());
+
+  const tilesetModel = {
+    on: vi.fn(),
+    off: vi.fn(),
+    send: vi.fn(),
+  };
+
+  const model: AnyModel<State> = {
+    get(key) {
+      const state: State = {
+        _plugin_urls: [],
+        _viewconf: {
+          views: [{
+            uid: "v",
+            layout: { x: 0, y: 0, w: 12, h: 6 },
+            tracks: {
+              top: [{ type: "top-axis", uid: "t" }],
+              center: [],
+              left: [],
+              right: [],
+              bottom: [],
+            },
+          }],
+        },
+        _options: {},
+        _tileset_client: "IPY_MODEL_fake",
+        location: [0, 0, 0, 0],
+      };
+      return state[key];
+    },
+    set: vi.fn(),
+    save_changes: vi.fn(),
+    on: vi.fn(),
+    off: vi.fn(),
+    send: vi.fn(),
+    widget_manager: {
+      get_model: vi.fn().mockResolvedValue(tilesetModel),
+    },
+  };
+
+  const cleanup = await widget.render({ model, el, experimental });
+
+  // resolved without throwing; container has content
+  expect(el.children.length).toBeGreaterThan(0);
+
+  expect(typeof cleanup).toBe("function");
+  cleanup?.();
+});
diff --git a/vite.config.mjs b/vite.config.mjs
new file mode 100644
index 0000000..ececcc6
--- /dev/null
+++ b/vite.config.mjs
@@ -0,0 +1,23 @@
+import { defineConfig } from "vitest/config";
+
+import { playwright } from "@vitest/browser-playwright";
+import deno from "@deno/vite-plugin";
+
+export default defineConfig({
+  plugins: [deno()],
+  test: {
+    globals: true,
+    browser: {
+      provider: playwright({
+        launchOptions: {
+          // needed to access WebGL in headless
+          args: ["--use-gl=angle", "--use-angle=swiftshader"],
+        },
+      }),
+      enabled: true,
+      instances: [
+        { browser: "chromium", headless: true },
+      ],
+    },
+  },
+});