To do so, you need to make your calculations conditional upon data type.
Minimize server requests by validating file size before uploading.
Using the Notificaitons API, you can send system-level notifications to a user.
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.
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.