Extend shinyjs by calling your own JavaScript functions

Add your own JavaScript functions that can be called from R as if they were regular R functions. This is a more advanced technique and can only be used if you know JavaScript. See 'Basic Usage' below for more information or view the shinyjs webpage to learn more.

extendShinyjs(script, text, functions)

Arguments

script: Path to a JavaScript file that contains all the functions. Each function name must begin with "shinyjs.", for example "shinyjs.myfunc". Note that the path to the file must be discoverable by the browser (meaning that it needs to be in a "www/" directory or available via addResourcePath()). See 'Basic Usage' below for more details.
text: Inline JavaScript code to use instead of providing a file. See 'Basic Usage' below.
functions: The names of the shinyjs JavaScript functions which are defined and you want to be able to call using shinyjs. For example, if you defined JavaScript functions named shinyjs.foo and shinyjs.bar, then use functions = c("foo", "bar").

Value

Scripts that are required by shinyjs.

Note

You still need to call useShinyjs() as usual, and the call to useShinyjs() must come before the call to extendShinyjs().

Basic Usage

Any JavaScript function defined in your script that begins with "shinyjs." and that's provided in the functions argument will be available to run from R using the "js$" variable. For example, if you write a JavaScript function called "shinyjs.myfunc" and used functions = c("myfunc"), then you can call it from R with js$myfunc().

It's recommended to write JavaScript code in a separate file and provide the filename as the script argument, but it's also possible to use the text argument to provide a string containing valid JavaScript code.

Here is a basic example of using extendShinyjs() to define a function that changes the colour of the page:

library(shiny)
library(shinyjs)

jsCode <- "shinyjs.pageCol = function(params){$('body').css('background', params);}"

shinyApp(
  ui = fluidPage(
    useShinyjs(),
    extendShinyjs(text = jsCode, functions = c("pageCol")),
    selectInput("col", "Colour:",
                c("white", "yellow", "red", "blue", "purple"))
  ),
  server = function(input, output) {
    observeEvent(input$col, {
      js$pageCol(input$col)
    })
  }
)

You can add more functions to the JavaScript code, but remember that every function you want to use in R has to have a name beginning with "shinyjs.". See the section on passing arguments and the examples below for more information on how to write effective functions.

Running JavaScript code on page load

If there is any JavaScript code that you want to run immediately when the page loads, you can place it inside a shinyjs.init function. The function shinyjs.init will automatically be called when the Shiny app's HTML is initialized. A common use for this is when registering event handlers or initializing JavaScript objects, as these usually just need to run once when the page loads. The functions parameter does not need to be told about the init function, so you can use an empty list such as functions = c() (or if you have an init function together with other shinyjs functions, simply list all the functions except for init).

For example, the following example uses shinyjs.init to register an event handler so that every keypress will print its corresponding key code:

jscode <- "
shinyjs.init = function() {
  $(document).keypress(function(e) { alert('Key pressed: ' + e.which); });
}"
shinyApp(
  ui = fluidPage(
    useShinyjs(),
    extendShinyjs(text = jscode, functions = c()),
    "Press any key"
  ),
  server = function(input, output) {}
)

Passing arguments from R to JavaScript

Any shinyjs function that is called will pass a single array-like parameter to its corresponding JavaScript function. If the function in R was called with unnamed arguments, then it will pass an Array of the arguments; if the R arguments are named then it will pass an Object with key-value pairs.

For example, calling js$foo("bar", 5) in R will call shinyjs.foo(["bar", 5]) in JS, while calling js$foo(num = 5, id = "bar") in R will call shinyjs.foo({num : 5, id : "bar"}) in JS. This means that the shinyjs.foo function needs to be able to deal with both types of parameters.

To assist in normalizing the parameters, shinyjs provides a shinyjs.getParams() function which serves two purposes. First of all, it ensures that all arguments are named (even if the R function was called without names). Secondly, it allows you to define default values for arguments.

Here is an example of a JS function that changes the background colour of an element and uses shinyjs.getParams().


shinyjs.backgroundCol = function(params) {
  var defaultParams = {
    id : null,
    col : "red"
  };
  params = shinyjs.getParams(params, defaultParams);

  var el = $("#" + params.id);
  el.css("background-color", params.col);
}

Note the defaultParams object that was defined and the call to shinyjs.getParams. It ensures that calling js$backgroundCol("test", "blue") and js$backgroundCol(id = "test", col = "blue") and js$backgroundCol(col = "blue", id = "test") are all equivalent, and that if the colour parameter is not provided then "red" will be the default.

All the functions provided in shinyjs make use of shinyjs.getParams, and it is highly recommended to always use it in your functions as well. Notice that the order of the arguments in defaultParams in the JavaScript function matches the order of the arguments when calling the function in R with unnamed arguments.

See the examples below for a shiny app that uses this JS function.