Perhaps the mastering shinybook should have posed a more complete reprex to consider ?
library(shiny)
ui <- fluidPage(
textInput("var","var","Sepal.Length"),
verbatimTextOutput("resulttext")
)
df <- iris
server <- function(input, output, session) {
var <- reactive(df[input$var])
range <- reactive(range(var(), na.rm = TRUE))
output$resulttext <- renderText({
req(range())
})
}
shinyApp(ui, server)
Warning: Error in range: unused arguments (var(), na.rm = TRUE)