using observeEvent for numericInput in shiny app - r

Question

I have a simple shiny app which I would like to show a warning if user input is bigger than a threshold.
library(shiny)
library(shinyalert)
ui <- fluidPage(
numericInput("obs", "Observations:", 1),
verbatimTextOutput("value")
)
server <- function(input, output) {
observeEvent(input$obs,{
if(!is.na(input$obs) && input$obs >10){
shinyalert("warning!", "input too big", type = "warning")
}
})
output$value <- renderText({ input$obs })
}
shinyApp(ui, server)
if user is not quick enough to provide input, let say for the input$obs = 110 we have 1 second delay between putting the second and third value the popups warning will appear !
How should I fix this ?

Answer 1

Use shinyCatch from spsComps to make your life easier
library(shiny)
library(spsComps)
ui <- fluidPage(
numericInput("obs", "Observations:", 1),
verbatimTextOutput("value")
)
server <- function(input, output) {
output$value <- renderText({
shinyCatch({
if(!is.na(input$obs) && input$obs >10) warning("input too big")
}, blocking_level = "warning", prefix = "")
input$obs
})
}
shinyApp(ui, server)
when blocking_level = "warning" is specified shinyCatch blocks following code in the renderText expression. So when your number is larger than 10, the new input$obs will not be rendered.
Here's what users see
Here's what developers see in the console

Answer 2

You can use showNotification() from shiny itself:
library(shiny)
ui <- fluidPage(
numericInput("obs", "Observations:", 1),
verbatimTextOutput("value")
)
server <- function(input, output) {
observeEvent(input$obs,{
if(!is.na(input$obs) && input$obs >10){
showNotification(
ui = tags$h4("Input Too Big!"),
type = "warning"
)
}
})
output$value <- renderText({ input$obs })
}
shinyApp(ui, server)
Or {shinytoastr}:
library(shiny)
library(shinytoastr)
ui <- fluidPage(
shinytoastr::useToastr(),
numericInput("obs", "Observations:", 1),
verbatimTextOutput("value")
)
server <- function(input, output) {
observeEvent(input$obs,{
if(!is.na(input$obs) && input$obs >10){
shinytoastr::toastr_warning(
message = "Decrease it.",
title = "Input too big!"
)
}
})
output$value <- renderText({ input$obs })
}
shinyApp(ui, server)
Or {spsComps} as #lz100 mentioned. The choice is yours.