shiny reactive log visualizer

[lgatto]

@lmsimp - this might be useful: from ?shiny::showReactLog:

Reactive Log Visualizer

Description:

     Provides an interactive browser-based tool for visualizing
     reactive dependencies and execution in your application.

Usage:

     showReactLog()

Details:

     To use the reactive log visualizer, start with a fresh R session
     and run the command ‘options(shiny.reactlog=TRUE)’; then launch
     your application in the usual way (e.g. using ‘runApp’). At any
     time you can hit Ctrl+F3 (or for Mac users, Command+F3) in your
     web browser to launch the reactive log visualization.

     The reactive log visualization only includes reactive activity up
     until the time the report was loaded. If you want to see more
     recent activity, refresh the browser.

     Note that Shiny does not distinguish between reactive dependencies
     that "belong" to one Shiny user session versus another, so the
     visualization will include all reactive activity that has taken
     place in the process, not just for a particular application or
     session.

     As an alternative to pressing Ctrl/Command+F3-for example, if you
     are using reactives outside of the context of a Shiny
     application-you can run the ‘showReactLog’ function, which will
     generate the reactive log visualization as a static HTML file and
     launch it in your default browser. In this case, refreshing your
     browser will not load new activity into the report; you will need
     to call ‘showReactLog()’ explicitly.

     For security and performance reasons, do not enable
     ‘shiny.reactlog’ in production environments. When the option is
     enabled, it's possible for any user of your app to see at least
     some of the source code of your reactive expressions and
     observers.