Imagine spotty, dropping connection, low bandwidth. You do not want to load big chunk of JS because it was never cached, or as Uber used to do, download all th

Imagine spotty, dropping connection, low bandwidth. You do not want to load big chunk of JS because it was never cached, or as Uber used to do, download all the possible new promos every time you opened the app... You want to squeeze through the minimal data you need to arrange your core business function.