Basically a single page request (that then immediately fetches all the associated JaveScript and CSS) to run the entire app.
It is popular now because its a very small step from that to having a PWA (progressive Web application) which is progressive in the sense that it can be completely cached on the users device, and work with no connection to the Internet.
It also improves page-load performance in connected situations by there being no pages to load (after the first one).
While a solid approach, SPAs can suffer from long initial load times, as well as a tendancy to suffer from complexity that comes with any monolithic large app.
Basically a single page request (that then immediately fetches all the associated JaveScript and CSS) to run the entire app.
It is popular now because its a very small step from that to having a PWA (progressive Web application) which is progressive in the sense that it can be completely cached on the users device, and work with no connection to the Internet.
It also improves page-load performance in connected situations by there being no pages to load (after the first one).
While a solid approach, SPAs can suffer from long initial load times, as well as a tendancy to suffer from complexity that comes with any monolithic large app.