Great question! I’ve run into this exact issue before when working with newer Font Awesome styles in Shiny. Here are a few straightforward ways to use fas, far, fal, and fab prefixes instead of the default fa:

Method 1: Directly Write HTML (No Dependencies) #

If you want full control without relying on package updates or extra libraries, just use Shiny’s HTML() function to manually define the icon element. This works with any Shiny version:

# Solid style left arrow with pull-right class
HTML('<i class="fas fa-angle-left pull-right"></i>')

# Regular style user icon
HTML('<i class="far fa-user"></i>')

# Brand style GitHub icon
HTML('<i class="fab fa-github"></i>')

This generates exactly the HTML you need—just swap out the prefix (fas/far/fal/fab) to match your desired style.

Method 2: Use Shiny's icon() Function (Cleaner Shiny Syntax) #

If you prefer to stick with icon() instead of raw HTML, you can adjust the parameters to override the default fa prefix:

Submethod 2.1: Manual Class Override #

Clear the default prefix parameter and specify the full class list directly:

icon("", prefix = "", class = "fas fa-angle-left pull-right")

• The first empty string skips the default icon name parsing
• prefix = "" prevents Shiny from adding the default fa- prefix
• The class parameter includes your desired style prefix, icon class, and any extra classes (like pull-right)

Submethod 2.2: Use bslib (Recommended for Bootstrap 5+) #

If you’re using Bootstrap 5 or later (via the bslib package), the icon() function gets a handy family parameter to specify Font Awesome styles directly. This is the cleanest approach:

1. First install bslib if you haven’t:

   install.packages("bslib")
   

2. Then use it in your app:

   library(shiny)
   library(bslib)
   
   ui <- page_fluid(
     # Bootstrap 5 theme auto-includes modern Font Awesome
     theme = bs_theme(version = 5),
     # Solid left arrow with pull-right
     icon("angle-left", family = "fas", class = "pull-right"),
     # Regular user icon
     icon("user", family = "far"),
     # Brand Twitter icon
     icon("twitter", family = "fab")
   )
   
   server <- function(input, output) {}
   
   shinyApp(ui, server)
   

   bslib handles loading the correct Font Awesome version, so you don’t have to worry about CDN links or compatibility.

Quick Note on Font Awesome Versions #

Keep in mind that fas/far/fal/fab are part of Font Awesome 5 and above. If you’re using an older Shiny setup without bslib, you’ll need to manually include the latest Font Awesome CSS in your UI:

tags$head(
  tags$link(rel = "stylesheet", href = "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.4.0/css/all.min.css")
)

内容的提问来源于stack exchange，提问作者Márcio Mocellin