Make bold text in HTML output R shiny

If you're not set on using the HTML function, I believe you should be able to use strong(paste(character_vector[index])) instead.

One more try, is this helpful?

require(shiny)

fruits <- c("banana","raccoon","duck","grapefruit")

runApp(list(ui = pageWithSidebar(
  headerPanel("Example"),
  sidebarPanel(
    sliderInput("index", 
                label = "Select a number",
                min = 1,
                max = 4,
                step = 1,
                value = 2)),
  mainPanel(
    htmlOutput("text")
  )),
  server = function(input, output) {
    output$text <- renderUI({
      fruits[input$index] <- paste("<b>",fruits[input$index],"</b>")
      HTML(paste(fruits))
    })
  }
))

This might help you:

shinyApp(
  ui <- basicPage(
    uiOutput(outputId = "text")

  ),
  server <- function(input,output){

    output$text <- renderText({
      HTML(paste0("<b>","bold","</b>", " not bold"))
    })

  })

Is that what you were looking for?