File structure

app/lib/mongodb.js

@@ -0,0 +1,29 @@
+import { MongoClient } from 'mongodb'
+
+const uri = process.env.MONGODB_URI
+const options = {}
+
+let client
+let clientPromise
+
+if (!process.env.MONGODB_URI) {
+  throw new Error('Please add your Mongo URI to .env.local')
+}
+
+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).
+  if (!global._mongoClientPromise) {
+    client = new MongoClient(uri, options)
+    global._mongoClientPromise = client.connect()
+  }
+  clientPromise = global._mongoClientPromise
+} 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
+// separate module, the client can be shared across functions.
+export default clientPromise