Problem

Shiny apps are, by default, a bit limited when looking at it from this perspective.  It can handle only GET requests by default, unless you are a technical expert in this field, see this stack overflow post. Furthermore shiny apps can have just one entry-point “/”. So you can’t have another entry-point “/page2”. Thus, the e-commerce shop is not possible out of the box in R shiny.

Solution

There are multiple solutions to support multiple pages. The one that I am using since a while is the package brochure developed by Colin Fay. It is still in development, so you might encounter some issues but I haven’t found any major bugs yet. A brochure app consists of a series of pages that are defined by an endpoint/path, a UI and a server function. Thus each page has its own shiny session, its own UI, and its own server! This is important to keep in mind.  A separate session for each page has some advantages but also some disadvantages (e.g. how to pass user data between pages?). A very simple brochureApp looks like this:

library(shiny)
library(brochure)

brochureApp(
  # First page
  page(
    href = "/",
    ui = fluidPage(
      h1("My first page"), 
      plotOutput("plot")
    ),
    server = function(input, output, session){
      output$plot <- renderPlot({
        plot(iris)
      })
    }
  ), 
  # Second page, no server-side function
  page(
    href = "/page2", 
    ui =  fluidPage(
      h1("My second page")
    )
  )
)

Donation app

Coming back to the E-commerce shop example, I have developed an app where one can sponsor me for my open source work on R packages. The app has an integration with Stripe to make a donation and a thank you and error page. When calling Stripe you have to give the two endpoints for these pages and by using brochure, I am able to setup these endpoints. See the app on shinyapps.io and of course I would appreciate it, if you use the app!:-)

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