R Shiny modal outputs render on input change strategies (previously rendered plot on input change visible VS plot render does not show previoous plot)

App1.R

# This app.R demonstrates how R Shiny rerenders a unique output id 
# the previously renred plot is initially visible, afterwards changed
# that is how shiny is designed to work

library(shiny)
library(ggplot2)

app <- shinyApp(
  ui = fluidPage(
    selectInput(
      "species",
      "Select spiecies",
      sort(unique(iris$Species)),
      "virginica"
    )
  ),
  server = function(input, output) {
    observeEvent(input$species, {
      showModal(
        modalDialog(
          textOutput("heading"),
          plotOutput("plot"),
          easyClose = TRUE,
          footer = NULL
        )
      )
    })

    output$heading <- renderText(input$species)

    output$plot <- renderPlot({
      ggplot(subset(iris, Species == input$species)) +
        geom_point(aes(Sepal.Length, Sepal.Width))
    })
  }
)

runApp(app)

App2.R

# if one wants not the previously displayed plot to initially reapear and then render the new plot
# one can crate with dedicated output ids for each of the plots (bound to the input).

library(shiny)
library(ggplot2)

species <- levels(iris$Species)

app <- shinyApp(
  ui = fluidPage(
    selectInput(
      "species", "Select spiecies", species, "virginica"
    )
  ),
  server = function(input, output) {
    observeEvent(input$species, {
      showModal(
        modalDialog(
          plotOutput(input$species),
          easyClose = TRUE,
          footer = NULL
        )
      )
    })
    
    lapply(species, function(x) {
      output[[x]] <- renderPlot({
        ggplot(subset(iris, Species == x)) +
          geom_point(aes(Sepal.Length, Sepal.Width))
      })
    })
    
  }
)

runApp(app)