This is an... interesting topic. Some people I talk to think that it's the best thing ever, while others think it's the worst, it's very controversial to say the least and opinion varies dramatically depending on the place, but they are getting a lot of momentum on the web.
Basically, you have a piece of JavaScript which loads a bunch of templates, and then, it fetches data from the server with a format like JSON. It can be used to build very snappy sites which have excellent perceived performance, but is incompatible with most ads (the biggest exception being Google Adwords).
Also, it might delay the initial page-load on mobile, and when resources are congested, most likely on a mobile device, it can make things feel fairly laggy due to all the extra JS being run.
In forums in particular, Discourse and NodeBB have jumped in head-first into it.
Basically, you have a piece of JavaScript which loads a bunch of templates, and then, it fetches data from the server with a format like JSON. It can be used to build very snappy sites which have excellent perceived performance, but is incompatible with most ads (the biggest exception being Google Adwords).
Also, it might delay the initial page-load on mobile, and when resources are congested, most likely on a mobile device, it can make things feel fairly laggy due to all the extra JS being run.
In forums in particular, Discourse and NodeBB have jumped in head-first into it.
