Embed reactively generated URL in shiny

Question

I would like to show in my shiny app a link that directs to the URL generated based on user's input. I don't want to show the full text of the URL. I know the a(href="",label="") function can be used if I know the URL beforehand, but in this case the URL depends on the user's input. The following doesn't work:

ui <- fluidPage(
    titlePanel("Show map of a given state"),
    sidebarLayout(
        sidebarPanel(
            textInput("state", label = "State", value = "CA", placeholder = "California or CA"),
            actionButton("showU","Show map")
        ),
        mainPanel(
            conditionalPanel(
                condition = "input.showU > 0",
                htmlOutput("url"),
                a(href=htmlOutput("url"),"Show in Google Map",target="_blank")
            )
        )
    )
)

server <- function(input, output){
    observeEvent(input$showU,{
    output$url <-renderUI({paste("https://www.google.com/maps/place/", input$state, sep="")})
    })
}

shinyApp(ui,server)

I hope I can click on the "Show in Google Map" and be directed to the URL generated on the fly. Please help me, thank you.

Answer 1

You need to use renderUI together with uiOutput to update UI reactively:

library(shiny)
ui <- fluidPage(
  titlePanel("Show map of a given state"),
  sidebarLayout(
    sidebarPanel(
      textInput("state", label = "State", value = "CA", placeholder = "California or CA"),
      actionButton("showU","Show map")
    ),
    mainPanel(
      conditionalPanel(
        condition = "input.showU > 0",
        uiOutput("url")
      )
    )
  )
)

server <- function(input, output){
  observeEvent(input$showU,{
    output$url <-renderUI(a(href=paste0('https://www.google.com/maps/place/', input$state),"Show in Google Map",target="_blank"))
  })
}

shinyApp(ui,server)