fix: Prevent MongoDB client promise being cached (#66977)

### What?
Update to
[examples/with-mongodb](https://github.com/vercel/next.js/tree/canary/examples/with-mongodb)
to incorporate fix from the MongoDB team. This should prevent
intermittent serverless function timeouts due to cached promise.

### Why?

Vercel users reported intermittent 500 errors when connecting to their
MongoDB Atlas clusters in production environments.

Full bug report: [NODE-6179](https://jira.mongodb.org/browse/NODE-6179)

Related issues:
- [10671](https://github.com/vercel/vercel/issues/10671)
- [5708](https://github.com/orgs/vercel/discussions/5708)
- [4297](https://github.com/orgs/vercel/discussions/4297)

### How?

Solution by @baileympearson – thank you 🖤

[View
commit](c08bc96353)
in `mongodb-developer/nextjs-with-mongodb`

---

- [x] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
- [x] Make sure the linting passes by running `pnpm build && pnpm lint`.
[See linting
docs](https://github.com/vercel/next.js/blob/canary/contributing/repository/linting.md).

examples/with-mongodb/lib/mongodb.ts

@@ -13,27 +13,24 @@ const options = {
   },
 };
 
-let client;
+let client: MongoClient;
-let clientPromise: Promise<MongoClient>;
 
 if (process.env.NODE_ENV === "development") {
   // In development mode, use a global variable so that the value
   // is preserved across module reloads caused by HMR (Hot Module Replacement).
   let globalWithMongo = global as typeof globalThis & {
-    _mongoClientPromise?: Promise<MongoClient>;
+    _mongoClient?: MongoClient;
   };
 
-  if (!globalWithMongo._mongoClientPromise) {
+  if (!globalWithMongo._mongoClient) {
-    client = new MongoClient(uri, options);
+    globalWithMongo._mongoClient = new MongoClient(uri, options);
-    globalWithMongo._mongoClientPromise = client.connect();
   }
-  clientPromise = globalWithMongo._mongoClientPromise;
+  client = globalWithMongo._mongoClient;
 } else {
   // In production mode, it's best to not use a global variable.
   client = new MongoClient(uri, options);
-  clientPromise = client.connect();
 }
 
-// Export a module-scoped MongoClient promise. By doing this in a
+// Export a module-scoped MongoClient. By doing this in a
 // separate module, the client can be shared across functions.
-export default clientPromise;
+export default client;

examples/with-mongodb/pages/index.tsx

@@ -1,5 +1,5 @@
 import Head from "next/head";
-import clientPromise from "../lib/mongodb";
+import client from "../lib/mongodb";
 import type { InferGetServerSidePropsType, GetServerSideProps } from "next";
 
 type ConnectionStatus = {
@@ -10,16 +10,7 @@ export const getServerSideProps: GetServerSideProps<
   ConnectionStatus
 > = async () => {
   try {
-    await clientPromise;
+    await client.connect(); // `await client.connect()` will use the default database passed in the MONGODB_URI
-    // `await clientPromise` will use the default database passed in the MONGODB_URI
-    // However you can use another database (e.g. myDatabase) by replacing the `await clientPromise` with the following code:
-    //
-    // `const client = await clientPromise`
-    // `const db = client.db("myDatabase")`
-    //
-    // Then you can execute queries against your database like so:
-    // db.find({}) or any of the MongoDB Node Driver commands
-
     return {
       props: { isConnected: true },
     };

examples/with-mongodb/types/mongodb.d.ts

@@ -1,5 +0,0 @@
-import { MongoClient } from "mongodb";
-
-declare global {
-  var _mongoClientPromise: Promise<MongoClient>;
-}