Not any more - once you can prerender the "SPA" on the server and use the same codebase to rehydrate it on the client and take over - which you can do today wit

Not any more - once you can prerender the "SPA" on the server and use the same codebase to rehydrate it on the client and take over - which you can do today with React and soon with Ember - then with the right setup the "progressive enhancement" bit can be "am I on the client now? let's do some extra stuff" implemented as part of the same component. e.g. here's a form that uses the same React component to render on the server, to handle regular form submissions and render redisplay when invalid and to progressively enhance with live validation and ajax form submission when JavaScript is available on the client: https://isomorphic-lab.herokuapp.com/add-thing https://isomorphic-lab.herokuapp.com/add-thing