reactlog: Reactive Log Visualizer

Description

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

Usage

reactlog()
reactlogShow(time = TRUE)
reactlogReset()
reactlogAddMark(session = getDefaultReactiveDomain())

Arguments

time: A boolean that specifies whether or not to display the time that each reactive takes to calculate a result.
session: The Shiny session to assign the mark to. Defaults to the current session.

Functions

reactlog(): Return a list of reactive information. Can be used in conjunction with reactlog::reactlog_show to later display the reactlog graph.
reactlogShow(): Display a full reactlog graph for all sessions.
reactlogReset(): Resets the entire reactlog stack. Useful for debugging and removing all prior reactive history.
reactlogAddMark(): Adds "mark" entry into the reactlog stack. This is useful for programmatically adding a marked entry in the reactlog, rather than using your keyboard's key combination.

For example, we can mark the reactlog at the beginning of an observeEvent's calculation:
```
observeEvent(input$my_event_trigger, {
  # Add a mark in the reactlog
  reactlogAddMark()
  # Run your regular event reaction code here...
  ....
})
```

Details

To use the reactive log visualizer, start with a fresh R session and run the command reactlog::reactlog_enable(); 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 reactlogShow 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 reactlogShow() explicitly.

For security and performance reasons, do not enable options(shiny.reactlog=TRUE) (or reactlog::reactlog_enable()) 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. In addition, reactlog should be considered a memory leak as it will constantly grow and will never reset until the R session is restarted.