An example of passing a json blob to the front-end from a Shiny app back-end.

server.R

library(shiny)
iris <- datasets::iris
names(iris) <- gsub('[/.]','_',tolower(names(iris)))

shinyServer(
  function(input, output) {
    output$json <- reactive({
      paste('<script>data=', 
            RJSONIO::toJSON(iris[iris$species == input$species,], byrow=T, colNames=T),
            ';console.log(data[0]);', # print 1 data line to console
            '</script>')
    })
  }
)

ui.R

require(shiny)
iris <- datasets::iris
names(iris) <- gsub('[/.]','_',tolower(names(iris)))
specs <- as.character(unique(iris$species))
names(specs) <- specs

pageWithSidebar(
  headerPanel("minimal json handling example"), 
  sidebarPanel(selectInput("species", "Species", specs)),
  mainPanel(
    htmlOutput("json")
  )
)