Where do I put the code for my own storage in Slingshot, in client, server or both?
You must add such files on the server only.
When you want to check where to put files when it is not documented you can try look into the package’s code:
For Slingshot you will see that similar “services” files are only loaded on the server:
api.add_files([ "lib/directive.js", "lib/storage-policy.js", "services/aws-s3.js", "services/google-cloud.js", "services/rackspace.js" ], "server");
Thank you. Good to know.