I don't really get this - it says you can use any npm dependency as well as access loca data. What do they mean by local data? Is there any persistency library for this e.g. to access a cloud sql database or a google big table instance?
*edit note: looks like you can definitely add more files via the package.json and import them as node modules, but I wouldn't rely on reading and writing from the file system.
As for persistency, if it's just Javascript code you can install node modules to accomplish what you want including talking to those cloud APIs. Unfortunately Bigtable might be the exception since I'm not sure if there's a good nodejs client yet (Bigtable only supports gRPC, not REST), but you could use Cloud Datastore instead.
Firebase will also be a very popular choice for persistence. Cloud Functions naturally complements Firebase to complete Backend-as-a-Service. The hope of Firebase is you don't need a server at all, but sometimes you have logic that really doesn't belong on a client (background jobs, "master" logic). Cloud Functions can fill in those gaps.
Firebase: https://www.firebase.com/
hand-rolled clients nodejs clients for google cloud apis: https://github.com/GoogleCloudPlatform/gcloud-node
auto-generated nodejs clients for google apis: https://github.com/google/google-api-nodejs-client
disclosure: work for GCP
I wasn't aware of those libraries for accessing Google cloud sql - so thanks for those.
After playing around with it, I'm not sure if the filesystem works, which makes sense given you just have a bucket or repo underneath and the code can be called at unpredictable times. You can, however, add additional javascript files via the package.json and import them, so if you can express your data as JSON or base64, you're good to go. Maybe there is a way to add other types of resources via the package.json but I haven't figured it out yet.
Generally you would interact with Cloud SQL using a regular node MySQL library, since it's just managed MySQL. The API would only be used to automate creating and setting up the CloudSQL instance.