Add JavaScript and CSS in Shiny

In this tutorial, I will cover how to include your own JavaScript, CSS and HTML code in your R shiny app. By including them, you can make a very powerful professional web app using R.

First let's understand the basics of a Webpage

In general, web page contains the following section of details.

Content (Header, Paragraph, Footer, Listing)
Font style, color, background, border
Images and Videos
Popups, widgets, special effects etc.

HTML, CSS and JavaScript

These 3 web programming languages in conjunction take care of all the information webpage contains (from text to adding special effects).

HTML determines the content and structure of a page (header, paragraph, footer etc.)
CSS controls how webpage would look like (color, font type, border etc.)
JavaScript decides advanced behaviors such as pop-up, animation etc.

Fundamentals of Webpage

One of the most common web development term you should know : rendering. It is the act of putting together a web page for presentation.

Shiny Dashboard Syntax

In this article, I will use shinydashboard library as it gives more professional and elegant look to app. The structure of shinydashboard syntax is similar to shiny library. Both requires ui and server components. However, functions are totally different. Refer the code below. Make sure to install library before using the following program.

# Load Library
library(shiny)
library(shinydashboard)

# User Interface
ui = 
  dashboardPage(
    dashboardHeader(title = "Blank Shiny App"),
    dashboardSidebar(),
    dashboardBody() 
    )

# Server
server = function(input, output) { }

# Run App
runApp(list(ui = ui, server = server), launch.browser =T)

Example : Create Animation Effect

The program below generates animation in the web page. To test it, you can check out this link. When user hits "Click Me" button, it will trigger demojs() JavaScript which will initiate animation. It's a very basic animation. You can edit the code and make it as complex as you want.

HTML

<p>
<button onclick='demojs()'>Click Me</button> </p>
<div id ="myContainer">
<div id ='sampleanimation'>
</div>
</div>

CSS

#sampleanimation {
width: 50px;
height: 50px;
position: absolute;
background-color: blue;
}

#myContainer {
  width: 400px;
  height: 400px;
  position: relative;
  background: black;
}

JS

function demojs() {
  var elem = document.getElementById('sampleanimation');   
  var position = 0;
  var id = setInterval(frame, 10);
  function frame() {
    if (position == 350) {
      clearInterval(id);
    } else {
      position++; 
      elem.style.top = position + 'px'; 
      elem.style.left = position + 'px'; 
    }
  }
}

There are several ways to include custom JavaScript and CSS codes in Shiny. Some of the common ones are listed below with detailed explanation -

Method I : Use tags to insert HTML, CSS and JS Code in Shiny

HTML

tags$body(HTML("Your HTML Code"))

CSS

tags$head(HTML("<style type='text/css'>
Your CSS Code
</style>"))

OR

CSS code can also be defined using tags$style.

tags$head(tags$style(HTML(" Your CSS Code ")))

tags$head(HTML("<script type='text/javascript'>
Your JS Code
</script>"))

OR

JS code can be described with tags$script.

tags$head(tags$script(HTML(" Your JS Code ")))

Code specified in tags$head means it will be included and executed under <head> </head>. Similarly tags$body can also be used to make shiny run code within <body> </body>

tags$head vs. tags$body

In general, JavaScript and CSS files are defined inside <head> </head>. Things which we want to display under body section of the webpage should be defined within <body> </body>.

Animation Code in Shiny

library(shiny)
library(shinydashboard)

# User Interface

ui <-

  dashboardPage(

    dashboardHeader(title = "Basic Use of JS and CSS"),

    dashboardSidebar(),

    dashboardBody(

   

  # Javasript Code

  tags$head(HTML("

  <script type='text/javascript'>

  function demojs() {

  var elem = document.getElementById('sampleanimation'); 

  var position = 0;

  var id = setInterval(frame, 10);

  function frame() {

    if (position == 350) {

      clearInterval(id);

    } else {

      position++;

      elem.style.top = position + 'px';

      elem.style.left = position + 'px';

    }

  }

}

</script>")),

   

# CSS Code

tags$head(HTML("

<style type='text/css'>

#sampleanimation {

width: 50px;

height: 50px;

position: absolute;

background-color: blue;

}

</style>")),

# HTML Code   

box(tags$body(HTML("<p>
<button onclick='demojs()'>Click Me</button> </p>
<div id ='sampleanimation'>
</div>
")), height = 400)

))

server = function(input, output) { }

runApp(list(ui = ui, server = server), launch.browser =T)

Important Note

In JS, CSS and HTML code, make sure to replace double quotation mark with single quotation mark under shiny's HTML(" ") function as it considers double quotation mark as closing the function.

Method II : Call JavaScript and CSS files in Shiny

You can use includeScript( ) and includeCSS( ) functions to refer JS and CSS codes from files saved in your local directory. You can save the files anywhere and mention the file location of them in the functions.

How to create JS and CSS files manually

Open notepad and paste JS code and save it with .js file extension and file type "All files" (not text document). Similarly you can create css file using .css file extension.

library(shinydashboard)

# User Interface
ui <- 
  dashboardPage(
    dashboardHeader(title = "Basic Use of JS and CSS"),
    dashboardSidebar(),
    dashboardBody(
      
  # Call Javasript and CSS Code from file
  tags$head(
  includeScript("C:\\Users\\DELL\\Documents\\animate.js"),
  includeCSS("C:\\Users\\DELL\\Documents\\animation.css")
  ),

# HTML Code      
box(tags$body(HTML("<p>
<button onclick='demojs()'>Click Me</button> </p>
<div id ='sampleanimation'>
</div>
")), height = 400)
))

server = function(input, output) { }

runApp(list(ui = ui, server = server), launch.browser =T)

When to use Method 2?

When you want to include a big (lengthy) JS / CSS code, use method 2. Method 1 should be used for small code snippets as RStudio does not support coloring and error-checking of JS / CSS code. Also it makes code unnecessary lengthy which makes difficult to maintain.

Method III : Add JS and CSS files under www directory

Step 1 :
Create an app using shinyApp( ) function and save it as app.R. Refer the code below.

library(shiny)
library(shinydashboard)

app <- shinyApp(
ui <- dashboardPage(
    dashboardHeader(title = "Basic Use of JS"),
    dashboardSidebar(),
    dashboardBody(
      
  # Javasript and CSS Code
  tags$head(tags$script(src='animate.js')),
  tags$head(tags$link(rel="stylesheet", type = "text/css", href = "animation.css")),
  
  # HTML Code
  box(tags$body(HTML("<p>
<button onclick='demojs()'>Click Me</button> </p>
<div id ='sampleanimation'>
</div>
")), height = 400)
))
,
server = function(input, output) { }
)

Step 2 :
Create a folder named www in your app directory (where your app app.r file is stored) and save .js and .css files under the folder. Refer the folder structure below.

├── app.R
└── www
    └── animate.js
    └── animation.css

Step 3 :
Submit runApp( ) function. Specify path of app directory.

runApp(appDir = "C:/Users/DELL/Documents", launch.browser = T)

Method IV : Using Shinyjs R Package

The shinyjs package allows you to perform most frequently used JavaScript tasks without knowing JavaScript programming at all. For example, you can hide, show or toggle element. You can also enable or disable input.

Example : Turn content on and off by pressing the same button

Make sure to install shinyjs package before loading it. You can install it by using install.packages("shinyjs").

Important Point : Use function useShinyjs( ) under dashboardBody( ) to initialize shinyjs library

library(shiny)
library(shinydashboard)
library(shinyjs)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    useShinyjs(),
    actionButton("button", "Click me"),
    div(id = "id1", "Sample Text")
  )
)

server <- function(input, output) {
  observeEvent(input$button, {
    toggle("id1")
  })
}

runApp(list(ui = ui, server = server), launch.browser =T)

In the above program, we have used toggle( ) function to turn content on and off.

Example : Enable or disable Numeric Input based on checkbox selection

library(shiny)
library(shinydashboard)
library(shinyjs)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    useShinyjs(),
    numericInput("sampleinput", "Categories", 1),
    checkboxInput("id1", label="Enable Input Box")
  ) 
  )
  
  server = function(input, output, session) {
    observeEvent(input$id1, {
      if(input$id1 == F){
        disable("sampleinput")
      } else {
        enable("sampleinput")
      }
    })
  }


runApp(list(ui = ui, server = server), launch.browser =T)

Communication between R and JavaScript

You can also define and call your own JavaScript function using shinyjs package with the use of extendShinyjs( ) function inside dashboardBody( ).

Make sure to define custom JavaScript function beginning with word shinyjs
JS function should be inside quotes
In server, you can call the function by writing js$function-name

The program below closes app when user clicks on action button.

library(shiny)
library(shinydashboard)
library(shinyjs)

jscode <- "shinyjs.exitWindow = function () {
  window.open('','_parent','');
  window.close();
}"

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    shinyjs::useShinyjs(),
    extendShinyjs(text = jscode),
    actionButton("close", "Close app")
  ) 
  )
  
  server = function(input, output, session) {
    observeEvent(input$close, {
      js$exitWindow();
    })
  }

runApp(list(ui = ui, server = server), launch.browser =T)

End Notes

With the huge popularity of JavaScript and many recent advancements, it is recommended to learn basics of JavaScript so that you can use them in R Shiny app. According to latest survey, JavaScript is used by 95% of websites. Its huge popularity is because of active broad JS developers community and being used by big players like Google, Facebook, Microsoft, etc.

Do comment on how you use shiny app in the comment box below. If you are beginner and want to learn building webapp using shiny, check out this tutorial

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About Author:

Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. He has over 7 years of experience in data science and predictive modeling. During his tenure, he has worked with global clients in various domains like banking, Telecom, HR and Health Insurance.

While I love having friends who agree, I only learn from those who don't.

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