library(shiny)
shinyApp(
  ui = fluidPage(
    div(id = "myapp",
      h2("shinyjs demo"),
      textInput("name", "Name", ""),
      numericInput("age", "Age", 30),
      textInput("company", "Company", ""),
      p("Timestamp: ", span(date())),
      actionButton("submit", "Submit")
    )
  ),
  
  server = function(input, output) {
  }
)

Add shinyjs features

Now suppose we want to add a few features to the app to make it a bit more user-friendly. First we need to set up the app to use shinyjs by making a call to useShinyjs() in the Shiny app’s UI.

Here are 7 features we’ll add to the app, each followed with the code to implement it using shinyjs:

1. The “Name” field is mandatory and thus the “Submit” button should not be enabled if there is no name

In the server portion, add the following code

observe({
  if (is.null(input$name) || input$name == "") {
    shinyjs::disable("submit")
  } else {
    shinyjs::enable("submit")
  }
})

Or instead you can use the toggleState function and pass it a condition:

observe({
  shinyjs::toggleState("submit", !is.null(input$name) && input$name != "")
})

You can use the optional condition in some other functions as well, which can be very useful to make your code shorter and more understandable.

2. The “Age” and “Company” fields are optional and we want to have the ability to hide that section of the form

First, we need to section off the “Age” and “Company” elements into their own section, so we surround them with a div

div(id = "advanced",
  numericInput("age", "Age", 30),
  textInput("company", "Company", "")
)

We also need to add a link in the UI that will be used to hide/show the section

a(id = "toggleAdvanced", "Show/hide advanced info")

Lastly, we need to tell Shiny to show/hide the section when the link is clicked by adding this code to the server

shinyjs::onclick("toggleAdvanced",
                  shinyjs::toggle(id = "advanced", anim = TRUE))

3. Similarly, since we don’t really care about “Age” and “Company” too much, we want to hide them initially when the form loads

Simply surround the section we want to hide initially with shinyjs::hidden

shinyjs::hidden(
  div(id = "advanced",
    ...
))

4. The user should be able to update the “Timestamp” in case he spends way too long filling out the form (not very realistic here, and the timestamp should ideally be determined when the button is clicked, but it’s good enough for illustration purposes)

First, we need to add an “Update” link to click on, and we need to give the element showing the time an id so that we can refer to it later when we want to change its contents.

To do that, replace p("Timestamp: ", span(date())) with

p("Timestamp: ", span(id = "time", date()), a(id = "update", "Update"))

Now we need to tell Shiny what to do when “Update” is clicked by adding this to the server

shinyjs::onclick("update", shinyjs::html("time", date()))

5. Some users may find it hard to read the small text in the app, so there should be an option to increase the font size

First, we need to add checkbox to the UI

checkboxInput("big", "Bigger text", FALSE)

In order to make the text bigger, we will use CSS. So let’s add an appropriate CSS rule by adding this code to the UI

shinyjs::inlineCSS(list(.big = "font-size: 2em"))

Lastly, we want the text to be big or small depending on whether the checkbox is checked by adding this code to the server

observe({
  if (input$big) {
    shinyjs::addClass("myapp", "big")
  } else {
    shinyjs::removeClass("myapp", "big")
  }
})

Or, again, we can use the toggleClass function with the condition argument:

observe({
  shinyjs::toggleClass("myapp", "big", input$big)
})

6. Give the user a “Thank you” message upon submission

Simply add the following to the server

observeEvent(input$submit, {
  shinyjs::alert("Thank you!")
})

7. Allow the user to reset the form

First let’s add a button to the UI

actionButton("reset", "Reset form")

And when the button is clicked, reset the form

observeEvent(input$reset, {
  shinyjs::reset("myapp")
})

Final code

The final code looks like this

library(shiny)
shinyApp(
  ui = fluidPage(
    shinyjs::useShinyjs(),
    shinyjs::inlineCSS(list(.big = "font-size: 2em")),
    div(id = "myapp",
        h2("shinyjs demo"),
        checkboxInput("big", "Bigger text", FALSE),
        textInput("name", "Name", ""),
        a(id = "toggleAdvanced", "Show/hide advanced info", href = "#"),
        shinyjs::hidden(
          div(id = "advanced",
            numericInput("age", "Age", 30),
            textInput("company", "Company", "")
          )
        ),
        p("Timestamp: ",
          span(id = "time", date()),
          a(id = "update", "Update", href = "#")
        ),
        actionButton("submit", "Submit"),
        actionButton("reset", "Reset form")
    )
  ),
  
  server = function(input, output) {
    observe({
      shinyjs::toggleState("submit", !is.null(input$name) && input$name != "")
    })
    
    shinyjs::onclick("toggleAdvanced",
                     shinyjs::toggle(id = "advanced", anim = TRUE))    
    
    shinyjs::onclick("update", shinyjs::html("time", date()))
    
    observe({
      shinyjs::toggleClass("myapp", "big", input$big)
    })
    
    observeEvent(input$submit, {
      shinyjs::alert("Thank you!")
    })
    
    observeEvent(input$reset, {
      shinyjs::reset("myapp")
    })    
  }
)

You can view the final app here.