Hot reloading Shiny apps

Fewer clicks and faster iteration

Goal

Faster development of shiny-related R packages through app hot reloading¹.

Problem

We build a Shiny app following this procedure:

1. Change the app code.

2. Launch it.

3. Interact with the app to bring it to a state that allows us to see the effects of the latest changes.

4. Evaluate the behavior of the app.

5. Close it and go all the way back to step 1 if we’re not done yet.

This launch-interact-close cycle is expensive, unnecessary friction. We could instead:

1. Launch the app [once].

2. Bring it to a state that allows us to see the effects of the changes we’re about to make [once].

3. Change the app code.

4. Evaluate the behavior of the app and go back to step 3 if we’re not done yet.

Traditional solution

• Use the shiny.autoreload option so that Shiny relaunches the app automatically whenever its code changes.

• Configure automatic bookmarking to preserve the application state across reloads.

Shortcomings of the traditional solution

• This approach does not work for modular Shiny applications prior to shiny 1.11.0. Thanks to the efforts of Garrick Aden-Buie, this is no longer an issue.

• This approach still fails to fully hot-reload applications developed as part of an R package.

• Manually adapting apps for hot-reloading is cumbersome. Cleaning the reloading-related code for publication is also a chore.

Proposed solution

Launch your unmodified Shiny app through our short and flexible app hot reloader script.

1. App reloading that preserves app state.