To do so, you need to make your calculations conditional upon data type.
Learn how for both an input the 'multiple' attribute and with multiple input elements.
First get the data in blob or blob-like format and then access its size property.
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.
After reading a file, you can display it, edit it, post it to a server and download.