sample shiny router app returning json but wrapped in websocket and html

shiny.router.dummy.R

# This was an attempt to return json on /health/ with shiny.router
# https://appsilon.com/shiny-router-package/
# trying https://stackoverflow.com/users/7268834/slavakx 's suggestion
# https://stackoverflow.com/questions/19991654/shiny-server-print-json-as-a-result-output 
# but the json is already wrapped
library(shiny)
library(shiny.router)
library(data.table)
library(jsonlite)

# This creates UI for each page.
page <- function(title, content) {
    
    div(
        shiny::sliderInput("int", "Choose integer:", -10, 10, 1, 1),
        titlePanel(title),
        p(content),
        uiOutput("power_of_input")
    )
}

# Part of both sample pages.
home_page <- page("Home page", "This is the home page!")
side_page <- verbatimTextOutput(outputId="jsonoutput")

# Callbacks on the server side for the sample pages
home_server <- function(input, output, session) {
    output$power_of_input <- renderUI({
        HTML(paste(
            "I display <strong>square</strong> of input and pass result to <code>output$power_of_input</code>: ", 
            as.numeric(input$int) ^ 2))
    })
}

side_server <- function(input, output, session) {
    output$jsonoutput <- renderText({
        
        #data <- getMainData()
        data <- data.table(a=1:3, b=sample(letters,3))
        
        result <- jsonlite::prettify(jsonlite::toJSON(data, auto_unbox = TRUE), 4)
        
        return(result)
    })
}

# Create routing. We provide routing path, a UI as well as a server-side callback for each page.
router <- make_router(
    route("home", home_page, home_server),
    route("side", side_page, side_server)
)

# Create output for our router in main UI of Shiny app.
ui <- shinyUI(fluidPage(
    router_ui()
))

# Plug router into Shiny server.
server <- shinyServer(function(input, output, session) {
    router(input, output, session)
})

# Run server in a standard way.
shinyApp(ui, server)