Covers: Chapter 18 - Shiny apps in packages

Shiny Apps

Code location and organization

• UI and server code for a submitted Shiny app must live under the package R/ directory (not in a top-level app.R / inst/shiny).
• Keep business logic out of shinyApp() calls. Build internal functions that generate UI and server components separately, so logic is testable without launching the app.
• Recommended file naming:
  • interface_*.R - functions returning UI elements
  • outputs_*.R - functions returning server outputs
  • observers_*.R - functions creating reactive observers
  • utils_*.R - misc processing helpers

Launching restrictions

• shiny::runApp() must NOT appear anywhere in the package source.
• Exported functions should RETURN a Shiny app object; the user calls runApp() themselves.

Testing

• Unit-test all non-reactive functions (e.g. with testthat).
• Wrap untestable reactive code with # nocov start / # nocov end.
• Use shinytest2 to test visual and computational aspects of the app.
• Put reusable test fixtures in tests/testthat/setup-*.R.

Documentation

• Wrap example code that launches an app in if (interactive()) { ... }.
• Document internal functions with roxygen2 @keywords internal.
• Include screenshots in the vignette; optimize with pngquant or webshot2.

Review expectations

• Reviewers run R CMD build, R CMD check, and BiocCheck, test the app with shinytest2, and check graceful error handling and responsive UI.

Source: Shiny apps Fetched 2026-08-14 from contributions.bioconductor.org (Bioconductor devel guide).