Responsiveness is excellent when your Julia process is on the same machine as the browser - which in itself addresses a large set of use cases scientific computing audience has (such as presentations). When the Julia process is connected over the network, there is obviously a lag between updates. But it's no better or worse than an AJAX/WebSocket application. The intention is to use web components to encapsulate UI components and their behavior (including self-contained animations) and Julia to read from them and update their attributes. So one can switch to writing web components and using them in Escher if responsiveness is really a concern. With the programming model in Escher, it will be easy to hoist some computations to the browser once there is Julia to JavaScript compilation. However, I don't plan to write the transpiler (yet) ;).