Using the Notificaitons API, you can send system-level notifications to a user.
Express provides a simple sytnax for creating a REST API in Node.js.
First get the data in blob or blob-like format and then access its size property.
You can combine lastIndexOf() and slice() to get the file extension.
Create a download indicator by reading the body of the response.
There is no native expiration option but it can be implemented using timestamps.
Pass a function through localStorage using the Function constructor object.
Allow your users to download any fetchable JSON file in CSV format.