Custom JavaScript, CSS and HTML in Shiny

December 23, 2018
By

(This article was first published on ListenData, and kindly contributed to R-bloggers)

In this tutorial, I will cover how to include custom 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 basics of a Webpage

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

  1. Content (Header, Paragraph, Footer, Listing)
  2. Font style, color, background, border
  3. Images and Videos
  4. 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).
  1. HTML determines the content and structure of a page (header, paragraph, footer etc.)
  2. CSS controls how webpage would look like (color, font type, border etc.)
  3. JavaScript decides advanced behaviors such as pop-up, animation etc.
Make JavaScript, CSS work for Shiny
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 section, I am using syntax of shinydashboard library. 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(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

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(“”))

OR

CSS code can also be defined using tags$style. 

tags$head(tags$style(HTML(” Your CSS Code “)))

JS

tags$head(HTML(“”))

OR

JS code can be described with tags$script.

tags$head(tags$script(HTML(” Your JS Code “)))

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

tags$head vs. tags$body

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

Animation Code in Shiny

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.

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.

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)

To leave a comment for the author, please follow the link and comment on their blog: ListenData.

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