Fix Mongoose example failed build due to env variable not found (verc…

…el#72918)

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Fixes vercel#72915 
Fix the `MONGODB_URI` env variable not found during `npm run build` by
moving the variable assignment to `dbConnect` function

Co-authored-by: Sam Ko <[email protected]>

examples/with-mongodb-mongoose/lib/dbConnect.ts

@@ -3,21 +3,21 @@ declare global {
   var mongoose: any; // This must be a `var` and not a `let / const`
 }
 
-const MONGODB_URI = process.env.MONGODB_URI!;
-
-if (!MONGODB_URI) {
-  throw new Error(
-    "Please define the MONGODB_URI environment variable inside .env.local",
-  );
-}
-
 let cached = global.mongoose;
 
 if (!cached) {
   cached = global.mongoose = { conn: null, promise: null };
 }
 
 async function dbConnect() {
+  const MONGODB_URI = process.env.MONGODB_URI!;
+
+  if (!MONGODB_URI) {
+    throw new Error(
+      "Please define the MONGODB_URI environment variable inside .env.local",
+    );
+  }
+
   if (cached.conn) {
     return cached.conn;
   }