Shiny Apps: is it possible to render HTML in validation messages? - r

Question

Is there any way to render HTML in shiny's validation messages? I tried different approaches using the HTML wrapper, the tags$... functions, as well as a separate htmlOutput for the validation message, but could not get any of them to work. Here is a simple example app that shows this issue - the select should be bold in the validation message but the HTML tags are escaped (contrived example, I know, but hopefully conveys the idea, I would primarily like to use this to include fa icons in the messages):
runApp(
list(
ui = fluidPage(
titlePanel("Validation App"),
sidebarLayout(
sidebarPanel(
selectInput("data", label = "Data set", choices = c("", "mtcars"))
),
mainPanel(tableOutput("table"))
)
),
server = function(input, output) {
data <- reactive({
# validate test
validate(
need(input$data != "", HTML("Please <strong>select</strong> a data set"))
)
get(input$data, 'package:datasets')
})
output$table <- renderTable(head(data()))
}
)
)

Answer 1

The simplest solution is to use a uiOutput and inside the renderUI function put an if to validate the input. In the code below is an example using HTML and tags$... functions. You can can also put an icon.
library(shiny)
runApp(
list(
ui = fluidPage(
titlePanel("Validation App"),
sidebarLayout(
sidebarPanel(
selectInput("data", label = "Data set", choices = c("", "mtcars"))
),
mainPanel(uiOutput("tableUI"))
)
),
server = function(input, output) {
data <- reactive({
get(input$data, 'package:datasets')
})
output$tableUI <- renderUI({
if (input$data == "") {
div(
HTML("Please <strong>select</strong> a data set"),
tags$p(icon("exclamation"), "Please",tags$strong("select"), "a data set")
)
} else {
tableOutput("table")
}
})
output$table <- renderTable(head(data()))
}
)
)