Reactive Expressions: Propagated Errors

Errors are propagated through the reactive graph just as values, but they present different behavior when they reach an:

• Output: The error will be displayed in the app.
• Observer: The error will cause the current session to terminate.
  • This can be avoided by wrapping the code in try() or tryCatch() functions.

From: examples/15-reactive-blocks/01-error-propagated-example.R

library(shiny)

ui <- fluidPage(
  checkboxInput("error", "error?"),
  textOutput("result")
)

server <- function(input, output, session) {
  a <- reactive({
    if (input$error) {
      stop("Error!")
    } else {
      1
    }
  })
  b <- reactive(a() + 1)
  c <- reactive(b() + 1)
  output$result <- renderText(c())
}

shinyApp(ui, server)