chore(react-sdk): adding vercel edge example (#1241)

This PR will add a vercel edge example showcasing that our Next.js
integration is compatible with the edge sdk (in fact it is almost
identical to the nodejs version)

### Caveat
I did not implement CI for this just yet. Still pending further
discussions to properly set things up.

### Alternative
This example might be able to replace the `complete` example we made for
`vercel` sdk.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Mostly adds a new example app and wiring in workspace/release config;
low blast radius outside docs/tooling. Risk is limited to potential
dependency/version drift in the new example and release-please
extra-files tracking.
> 
> **Overview**
> Adds a new `packages/sdk/react/examples/vercel-edge` Next.js App
Router example demonstrating flag evaluation via
`@launchdarkly/vercel-server-sdk` + Vercel Edge Config, with server-side
`createLDServerSession`/`useLDServerSession` and client bootstrap
through `LDIsomorphicProvider`.
> 
> Updates the monorepo to include the example in Yarn workspaces,
documents it in the React examples README, adds a basic Playwright e2e
check, and extends `release-please-config.json` to keep the example’s
`@launchdarkly/react-sdk` and `@launchdarkly/vercel-server-sdk`
dependency pins in sync.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
26b0092. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

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Author: joker23

package.json

@@ -22,6 +22,7 @@
     "packages/sdk/react/contract-tests",
     "packages/sdk/react/examples/hello-react",
     "packages/sdk/react/examples/react-server-example",
+    "packages/sdk/react/examples/vercel-edge",
     "packages/sdk/react-native",
     "packages/sdk/react-native/example",
     "packages/sdk/react-native/contract-tests/entity",

packages/sdk/react/examples/README.md

@@ -6,3 +6,4 @@ This directory contains example applications demonstrating the LaunchDarkly Reac
 |---------|-------------|
 | [hello-react](./hello-react/) | Minimal Vite + React app that evaluates a boolean feature flag and displays the result with real-time updates. This is the recommended starting point. |
 | [react-server-example](./react-server-example/) | Next.js App Router example demonstrating server-side flag evaluation with React Server Components. |
+| [vercel-edge](./vercel-edge/) | Next.js App Router example using the Vercel Edge SDK to evaluate flags from Vercel Edge Config, with server-to-client bootstrap via `LDIsomorphicProvider`. |

packages/sdk/react/examples/vercel-edge/.gitignore

@@ -0,0 +1,43 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# testing
+/coverage
+/test-results
+
+# next.js
+/.next/
+/out/
+/.swc/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# env files (can opt-in for committing if needed)
+.env*
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts

packages/sdk/react/examples/vercel-edge/README.md

@@ -0,0 +1,84 @@
+# LaunchDarkly sample React + Vercel Edge application
+
+We've built a simple web application that demonstrates how the LaunchDarkly React SDK works with
+the Vercel Edge SDK. The app evaluates feature flags using data stored in
+[Vercel Edge Config](https://vercel.com/docs/edge-config/overview) and renders the result using
+React Server Components.
+
+The Vercel SDK reads flag data from Edge Config instead of connecting to LaunchDarkly servers
+directly, providing ultra-low latency flag evaluation at the edge.
+
+The demo shows 2 ways to use React server-side rendering:
+
+1. Using `createLDServerSession` and `useLDServerSession` to provide
+per-request session isolation: Nested Server Components access the session through React's `cache()`
+without any prop drilling.
+
+2. Using the `LDIsomorphicProvider` to bootstrap the browser SDK with server-evaluated flag values.
+This allows the browser SDK to start immediately with real values.
+
+Below, you'll find the build procedure. For more comprehensive instructions, you can visit your
+[Quickstart page](https://app.launchdarkly.com/quickstart#/) or the
+[React SDK reference guide](https://docs.launchdarkly.com/sdk/client-side/react/react-web).
+
+This demo requires Node.js 18 or higher.
+
+## Prerequisites
+
+This example requires the [LaunchDarkly Vercel integration](https://vercel.com/integrations/launchdarkly)
+to be configured. The integration syncs your LaunchDarkly flag data to Vercel Edge Config so that
+the Vercel SDK can read it without connecting to LaunchDarkly servers.
+
+## Build instructions
+
+1. Set the `VERCEL_EDGE_CONFIG` environment variable to your Vercel Edge Config connection string.
+   You can find this in your Vercel project settings under Edge Config.
+
+   ```bash
+   export VERCEL_EDGE_CONFIG="https://edge-config.vercel.com/ecfg_..."
+   ```
+
+2. Set the `LD_CLIENT_SIDE_ID` environment variable to your LaunchDarkly client-side ID.
+   The Vercel SDK uses this to look up flag data in Edge Config, and the same value is used
+   to bootstrap the browser SDK.
+
+   ```bash
+   export LD_CLIENT_SIDE_ID="my-client-side-id"
+   ```
+
+3. If there is an existing boolean feature flag in your LaunchDarkly project that you want to
+   evaluate, set `LAUNCHDARKLY_FLAG_KEY`:
+
+   ```bash
+   export LAUNCHDARKLY_FLAG_KEY="my-flag-key"
+   ```
+
+   Otherwise, `sample-feature` will be used by default.
+
+## Running
+
+On the command line, run:
+
+```bash
+yarn dev
+```
+
+Then open [http://localhost:3000](http://localhost:3000) in your browser. You will see the
+spec message, current context name, and a full-page background: green when the flag is on,
+or grey when off.
+
+To simulate a different user, append the `?context=` query parameter. Each tab gets a
+completely independent `LDServerSession` with its own context:
+
+| URL | Context |
+|-----|---------|
+| `http://localhost:3000/` | Sandy (example-user-key) — default |
+| `http://localhost:3000/?context=sandy` | Sandy (example-user-key) |
+| `http://localhost:3000/?context=jamie` | Jamie (user-jamie) |
+| `http://localhost:3000/?context=alex` | Alex (user-alex) |
+
+If you have targeting rules in LaunchDarkly that serve different values to different user keys,
+you will see different flag results for each context.
+
+In a production app, the user identity would come from auth tokens, cookies, or session data
+instead of query parameters.

packages/sdk/react/examples/vercel-edge/app/App.tsx

@@ -0,0 +1,41 @@
+import { useLDServerSession } from '@launchdarkly/react-sdk/server';
+
+import BootstrappedClient from './BootstrappedClient';
+
+// The flag key to evaluate. Override with the LAUNCHDARKLY_FLAG_KEY environment variable.
+const flagKey = process.env.LAUNCHDARKLY_FLAG_KEY || 'sample-feature';
+
+export default async function App() {
+  // The session was stored here by createLDServerSession() in the parent page.
+  const session = useLDServerSession();
+
+  if (!session) {
+    return (
+      <p className="no-session">
+        No LaunchDarkly session found. Ensure createLDServerSession() is called before rendering
+        this component.
+      </p>
+    );
+  }
+
+  const flagValue = await session.boolVariation(flagKey, false);
+  const ctx = session.getContext() as { name?: string; key: string };
+
+  console.log('[LaunchDarkly] Flag evaluation:', {
+    flagKey,
+    flagValue,
+    context: session.getContext(),
+  });
+
+  return (
+    <div className={`app ${flagValue ? 'app--on' : 'app--off'}`}>
+      <p className="flag-key">Feature flag: {flagKey}</p>
+      <p className="context">Context: {ctx.name ?? ctx.key}</p>
+      <p>
+        <strong>Server:</strong> feature flag evaluates to {String(flagValue)} (server-side
+        rendered).
+      </p>
+      <BootstrappedClient flagKey={flagKey} />
+    </div>
+  );
+}

packages/sdk/react/examples/vercel-edge/app/BootstrappedClient.tsx

@@ -0,0 +1,18 @@
+'use client';
+
+import { useBoolVariation } from '@launchdarkly/react-sdk';
+
+/**
+ * Client component that evaluates a flag via the bootstrapped react clientSDK.
+ * The LDIsomorphicProvider evaluates all flags on the server and passes them
+ * to the react client SDK as bootstrap data.
+ */
+export default function BootstrappedClient({ flagKey }: { flagKey: string }) {
+  const flagValue = useBoolVariation(flagKey, false);
+
+  return (
+    <p>
+      <strong>Client:</strong> feature flag evaluates to {String(flagValue)} (bootstrapped).
+    </p>
+  );
+}

packages/sdk/react/examples/vercel-edge/app/layout.tsx

@@ -0,0 +1,13 @@
+import './styles.css';
+
+export default function RootLayout({
+  children,
+}: Readonly<{
+  children: React.ReactNode;
+}>) {
+  return (
+    <html lang="en">
+      <body>{children}</body>
+    </html>
+  );
+}

packages/sdk/react/examples/vercel-edge/app/page.tsx

@@ -0,0 +1,81 @@
+import { createClient } from '@vercel/edge-config';
+
+import { createLDServerSession, LDIsomorphicProvider } from '@launchdarkly/react-sdk/server';
+import { init } from '@launchdarkly/vercel-server-sdk';
+
+import App from './App';
+
+// The Vercel SDK reads flag data from Vercel Edge Config instead of connecting
+// to LaunchDarkly servers directly, so it uses the client-side ID — not the
+// server SDK key.
+const clientSideId = process.env.LD_CLIENT_SIDE_ID || '';
+const edgeConfig = process.env.VERCEL_EDGE_CONFIG;
+const edgeConfigClient = edgeConfig ? createClient(edgeConfig) : null;
+const ldBaseClient = clientSideId && edgeConfigClient ? init(clientSideId, edgeConfigClient) : null;
+
+// Select via ?context=sandy|jamie|alex (defaults to sandy).
+const PRESET_CONTEXTS = {
+  sandy: { kind: 'user' as const, key: 'example-user-key', name: 'Sandy' },
+  jamie: { kind: 'user' as const, key: 'user-jamie', name: 'Jamie' },
+  alex: { kind: 'user' as const, key: 'user-alex', name: 'Alex' },
+};
+
+export default async function Home({
+  searchParams,
+}: {
+  searchParams: Promise<{ context?: string }>;
+}) {
+  if (!edgeConfigClient) {
+    return (
+      <div className="error">
+        <p>
+          Vercel Edge Config is required: set the VERCEL_EDGE_CONFIG environment variable and try
+          again.
+        </p>
+      </div>
+    );
+  }
+
+  if (!ldBaseClient) {
+    return (
+      <div className="error">
+        <p>
+          LaunchDarkly client-side ID is required: set the LD_CLIENT_SIDE_ID environment variable
+          and try again.
+        </p>
+      </div>
+    );
+  }
+
+  try {
+    await ldBaseClient.waitForInitialization();
+  } catch {
+    return (
+      <div className="error">
+        <p>
+          SDK failed to initialize. Please check your Edge Config connection and LaunchDarkly
+          client-side ID for any issues.
+        </p>
+      </div>
+    );
+  }
+
+  // Resolve the evaluation context from the ?context= query parameter.
+  // In a real app this would come from authentication tokens, cookies, or session data.
+  const { context: contextKey = 'sandy' } = await searchParams;
+  const context =
+    PRESET_CONTEXTS[contextKey as keyof typeof PRESET_CONTEXTS] ?? PRESET_CONTEXTS.sandy;
+
+  // Create a per-request session bound to this user's context.
+  // createLDServerSession also stores the session in React's cache() so any Server Component
+  // in this render tree can retrieve it via useLDServerSession().
+  const session = createLDServerSession(ldBaseClient, context);
+
+  // Wrap the app with LDIsomorphicProvider to bootstrap the browser SDK with
+  // server-evaluated flag values.
+  return (
+    <LDIsomorphicProvider session={session} clientSideId={clientSideId}>
+      <App />
+    </LDIsomorphicProvider>
+  );
+}

packages/sdk/react/examples/vercel-edge/app/styles.css

@@ -0,0 +1,50 @@
+*,
+*::before,
+*::after {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+/* ── Error states (page.tsx) ───────────────────────── */
+.error {
+  min-height: 100vh;
+  background-color: #373841;
+  color: #ffffff;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 2rem;
+}
+
+/* ── App ──────────────────────────────────────────── */
+.no-session {
+  color: #ff6b6b;
+  font-family: monospace;
+}
+
+.app {
+  min-height: 100vh;
+  color: #ffffff;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
+  font-size: calc(10px + 2vmin);
+  padding: 2rem;
+  gap: 1rem;
+}
+
+.app--on {
+  background-color: #00844b;
+}
+.app--off {
+  background-color: #373841;
+}
+
+.context,
+.flag-key {
+  font-size: 0.7em;
+  opacity: 0.75;
+}

packages/sdk/react/examples/vercel-edge/e2e/verify.spec.ts

@@ -0,0 +1,9 @@
+import { expect, test } from '@playwright/test';
+
+test('feature flag evaluates to true', async ({ page }) => {
+  await page.goto('/');
+
+  await expect(page.getByText('feature flag evaluates to true', { exact: false })).toHaveCount(2, {
+    timeout: 10000,
+  });
+});