How do you use addResourcepath() in R Shiny?

Question

I'm struggling to understand how to use the addResourcePath() function from R shiny (https://shiny.rstudio.com/reference/shiny/latest/resourcePaths.html), even despite this apparent solution to someone with a similar question How do I porperly use addResourcePath?

I want to refer to a folder containing several javascript files to be used in my shiny app, but I don't understand what the 'prefix' is supposed to be, nor how to get the 'directory path'. How does one use addResourcePath to give R Shiny access to files in a particular folder?

score 6 · Accepted Answer · answered Nov 30 '21 at 07:27

Here is a basic explanation in simple words.

Assuming you want to add the file myScript.js located in c:/javascript_files. The simplest solution would be to copy myScript.js to a www subdirectory where your app is located. Anything located in www can be accessed by the UI of your app by using the prefix /.

For this example to add your script to the UI you can use

tags$head(tags$script(src="myScript.js")))

The HTML code generated by Shiny is going to be

<script src="myScript.js"></script>

Your browser is going to interpret it as http://your_site/myScript.js. Here the prefix is just /.

But in the case you want to keep your JS code in the original location (c:/javascript_files), you need to make it accessible to the UI (front-end) of your app. Since you can not use a URL like http://your_site/c:/javascript_files/myScript.js, you need to create a "virtual" subdirectory that is mapping your local directory to a URL directory, that is actually the prefix parameter in addResourcePath().

For this example, lets use as prefix jscode. The expression:

addResourcePath("jscode", "c:/javascript_files")

is going to create a "virtual" directory named jscode to be used in the URL of your app for the local directory c:/javascript_files.

The expression:

tags$head(tags$script(src="jscode/myScript.js")))

is going to be translated to HTML as

<script src="jscode/myScript.js"></script>

which is going to be interpreted by the browser as http://your_site/jscode/myScript.js.

If you had a subdirectory like c:/javascript_files/code_a, you don't need to add it, you can reference it in the same way like:

<script src="jscode/code_a/myScript.js"></script>

The Shiny code to add the myScript.js file will be:

library(shiny)

addResourcePath("jscode", "c:/javascript_files")

ui <- fluidPage(
  tags$head(tags$script(src = "jscode/myScript.js"))  
)

server <- function(input, output, session) {
}

shinyApp(ui, server)

Thanks for your very detailed response @Geovany. So prefix does not actually refer to anything specific, but is just a name you are providing that you will refer to later when you want to pull a file from the location? — Jamie, Dec 01 '21 at 15:55
You can see the prefix as an alias to refer to your local directory. — Geovany, Dec 01 '21 at 19:54
Very helpful, you did a nice job of explaining the prefix. I flailed around for a long time using the package resource materials and they were useless. Thanks for taking the time to patiently explain to us newbies — Village.Idyot, Oct 18 '22 at 18:10

How do you use addResourcepath() in R Shiny?

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