Installing R Packages

WebR supports the loading of R packages that have been pre-compiled targeting WebAssembly.

WebR packages must be installed before use, which in practice means copying binaries into the webR virtual filesystem in some way, either as part of the webR build process or during runtime by downloading packages from a repository or mounting filesystem data.

Downloading packages from a webR binary repository

A collection of supported packages are publicly hosted via a CDN in a CRAN-like repository with URL,

The public CDN build of webR has been distributed with a pre-installed webr support package. This R package provides a helper function install(), which can be used to install further R packages from a compatible webR binary repository.

The repository URL is set using the repos argument and the public build of webR defaults this argument to the repository URL shown above1.

Example: Installing the Matrix package

Run the following R code in a running webR session, such as the webR REPL demo,


If the package is available for webR and downloads successfully, you can then load the package in the usual way.


Shimming install.packages() for webR

The webr support package includes the function shim_install() which optionally replaces specific base R functions with implementations that work in the webR environment. Once executed, the base R install.packages() function can be used to install webR packages.


The webR REPL demo performs this base R function replacement as part of its startup procedure.

Interactively installing packages

The webr support package provides an optional global handler that will show an interactive prompt whenever loading a library fails, asking the user if they would like to try downloading the package from the configured default webR binary package repository.


As part of its startup, the webR REPL demo enables this handler. Once enabled, it is possible to install and load packages interactively via a prompt. The process is as follows,

Failed to load package "Matrix". Do you want to try downloading
it from the webR binary repo?
  1: Yes
  2: No
Selection: 1
Downloading webR package: lattice
Downloading webR package: Matrix

Once the package has been downloaded in this way, the next call to library() will load the package as usual.

Installing packages from JavaScript

The webR JavaScript API provides the function WebR.installPackages(). This convenience function takes an array of packages as its only argument and for each calls install() with the default webR binary package repository.

await webR.installPackages(['Matrix', 'cli'])

Once the promise returned by WebR.installPackages() has resolved, the packages can be loaded in the usual way using library().

Mounting an R library filesystem image

R libraries that have been packaged with Emscripten’s file_packager tool may be loaded into the webR virtual filesystem (VFS) by mounting the image using webr::mount(). When using webR in a browser, type = "WORKERFS" (the default) should be used so that the filesystem image is downloaded from the URL given by source and mounted on the VFS at mountpoint.

  mountpoint = "/library",
  source = ""

Once the library filesystem image has been mounted, the base R .libPaths() function should be used to ensure mountpoint is included in R’s package library search path.

.libPaths(c(.libPaths(), "/library"))

Packages that exist in the R library filesystem image can then be loaded as normal.


Details on how to build a WebAssembly R package library can be found in the Building R Packages section, and further information about mounting data to the VFS (including when running under Node.js) can be found in the Mounting Filesystem Data section.


  1. Other R package repositories providing WebAssembly binaries are also available, such as R-universe.↩︎