Shiny app skeleton with a loading screen that aims to minimize the time to first contentful paint (FCP).

Demo: https://nanx.shinyapps.io/shiny-fcp-loader/

Blog post: https://nanx.me/blog/post/shiny-fcp-loader/

For larger Shiny apps, users could wait a long time with a blank screen before seeing the rendered app content in the web browser, possibly due to:

• Loading a considerable number of render-blocking CSS/JS dependencies.
• Initializing the app state with some intensive computation.
• Connecting to servers with bandwidth and response time limitations.

This Shiny app skeleton solves these problems on the app code level by:

• Implement a loading screen (loader); hide it after the main UI resources are loaded, and the state initialization is finished.
• Prioritizing loading the loader code so it can render before the main UI assets.
• Loading the main UI assets later separately without blocking the rendering of the loader.

• The general structure of the loading screen code is from scartwright91/loading-dashboard, by using the single-element CSS spinner from Luke Haas and shinyjs from Dean Attali.
• The loader code is packed as HTML dependency following the guidelines in the handle HTML dependencies with htmltools chapter of the "Outstanding User Interfaces with Shiny" book by David Granjon.