There seems to be no API for downloading files to the phone in the framework. I want to download files in the app and save them in the storage space of the phone. How can this function be implemented roughly?
In two parts. First you need to download, and then you need a way to save to phone storage.
For the downloading part, Framework7 has its own request library https://framework7.io/docs/request.html
For saving to phone storage, if you’re using Cordova you can just use cordova-plugin-file.