johnhungerford / sbt-jsbundler   0.0.4

MIT License GitHub

An extensible sbt plugin to bundle Scala.js projects with non-Scala dependencies

Scala versions: 2.12
sbt plugins: 1.0


An extensible sbt plugin for bundling Scala.js with non-Scala dependencies. Currently supports vite.

Informed largely by


This plugin requires sbt 1.0.0+.

To use sbt-vite in your project, add the following line to projects/plugins.sbt:

addSbtPlugin("io.github.johnhungerford" % "sbt-jsbundler" % "0.0.4")

In build.sbt, include JSBundlerPlugin in .enablePlugins(...) in any Scala.js project that needs to be bundled with JavaScript dependencies. Add the following setting to your jsbundler project as well:

bundlerManagedSources ++= Seq(

where Seq(...) contains a list of directories and files that should be included in your bundle. This should include your package.json/package-lock.json as well as your any assets and non-Scala source you want to include.


Add the following files on of your bundlerManagedSources directories in your project or sub-project:


<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <script type="module" src="/main.js"></script>

If your Scala.js project is runnable (i.e., if it has a def main entrypoint and scalaJSUseMainModuleInitializer := true in build.sbt), you can simply import the application to be run as follows:


// 'scalajs:' will be resolved by vite to the output of the Scala.js linker
import 'scalajs:'

Otherwise you can import any exported objects from your Scala.js project as follows:


import { someLib, otherLib } from 'scalajs:';




Once you have your html and js entrypoints in place, you can run the following to generate a web bundle:

sbt bundle

This will compile your project, generate an appropriate vite configuration, and run vite on all artifacts. By default, the bundle will persisted at [project-directory]/target/scala-[x.x.x]/jsbundler-opt/dist. Use sbt fastLinkJS/bundle to run build in development mode and skip optimizations.

To launch a development server, you can run:

sbt "~startDevServer" stopDevServer

or generate a script to launch a dev server without having to use the sbt console:

sbt generateDevServerScript

This will output a shell script at your project root. It's recommended to use this script to launch the dev server rather than sbt so that you can use your sbt console to run ~prepareBundlerSources. This will update your build as you edit your Scala.js files so that vite can reload the page.


Run tests using the usual command:

sbt test

This will use vite to bundle the linked JavaScript test executable with any dependencies prior to running it.

Dependency management

This plugin would not be of much use if it did not resolve dependencies properly. One of the advantages of sbt-jsbundler is that it provides a consistent pattern for resolving imports in both your Scala.js and your JS/TS code.

NPM dependencies

As long as package.json is included in your bundlerManagedSources, jsbundler will be able to resolve any usual npm package imports, both in your Scala.js and JS/TS code.

Other non-Scala.js sources

In addition to bundling npm modules, sbt-jsbundler will bundle Scala.js outputs with local imports, such as JavaScript, TypeScript, css, less, and others.

Source files and directories should be declared for inclusion using the bundlerManagedSources setting:

bundlerManagedSources := Seq(

In the above scenario, some TypeScript and CSS sources are included from sub-project source directories, while others are included from a common source directory at the project root.

For any declared source that points to a directory, sbt-jsbundler will copy all the files and directories within it to the build directory prior to running vite. Any declared source that is a file will be copied directly to the build directory.

Accordingly, any sources declared in your build can be imported as expected:

// This will import either from [project]/src/main/typescript/someDir/someTypeScriptModule.ts
// or from common/typescript/someDir/someTypeScriptModule.ts
@JSImport("/someDir/someTypeScriptModule", JSImport.Default)
object TypeScriptImport extends js.Object

// This will import either from [project]/src/main/styles/someStyle.css or from
// common/styles/someStyle.css
@JSImport("/someStyle.css?inline", JSImport.Namespace)
object CssImport extends js.Object

These imports will work correctly in JS and TS sources as well:

import someModule from '/someDir/someTypeScriptModule';
import '/someStyle.css';

Importing Scala.js outputs

To import Scala.js artifacts into JS/TS sources, simply prefix the imported path with scalajs:.

For example, if you Scala.js codebase includes the following export:

JSExportTopLevel("myExportedFunction", "myModule")
def myExportedFunction(i: Int, j: Int): Int = ???

You would import it in a JavaScript file as follows:

import { myExportedFunction } from 'scalajs:myModule.js';

Note that if the moduleId "myModule" is left out of JSExportTopLevel(), it will be exported from a main.js script. Imports from main.js do not need to be stated explicitly, so you could just import it as:

import { myExportedFuction } from 'scalajs:';

Note the colon is still required to for the plugin to resolve it correctly.

Build command customization

To customize the commands used to execute the various vite tasks supported by sbt-jsbundler, you can configure the bundler implementation:

fastLinkJS / bundlerImplementation := sbtjsbundler.vite.ViteJSBundler(
        .addEnv("NODE_ENV" -> "development") // This can be necessary for testing

Note that we have only scoped the above implementation for fastLinkJS, which means it will only apply to development builds. fullLinkJS / bundlerImplementation will retain the default value, which is ViteJSBundler(ViteJSBundler.Config()).

You can similarly add arguments and environment variables to the npm install commands by customizing bundlerNpmManager:

bundlerNpmManager := NpmManager(

Vite config overrides

The vite implementation of sbt-jsbundler generates configuration scripts with reasonable defaults for full builds (i.e., bundle, which is an alias for Compile / fullLinkJS/ bundle), development builds (i.e., fastLinkJS / bundler), and test builds (i.e., Test / fastLinkJS / bundle, which prepares a bundle to be executed by Test / test).

To override these defaults, you can use the setting bundlerConfigSources to provide one or more configuration scripts that will be merged with the defaults, allowing you to override various settings. Note that the following configuration properties cannot be overridden:

  1. root
  2. build.outDir
  3. build.rollupOptions.input (for tests only)

bundlerConfigSources must specify valid javascript files that provide a default export of one of the following two forms:

  1. a simple vite configuration object
  2. a function that consumes a vite environment configuration and returns a vite configuration.

Note that neither of these should be wrapped in defineConfig, as this will be called after merging imported overrides.

Note also that the viteConfigSources will be merged in order, so later sources in the Seq will have precedence over prior sources.

bundlerConfigSources can be scoped to both Compile/Test and fullLinkJS/fastLinkJS to provide different customizations for different build types.


The following vite config source provides overrides to support JSX (React), bundle source maps (disabled by default except in tests), and break out several library dependencies into separate chunks:


bundlerConfigSources += file("vite.config-build.js")


import react from '@vitejs/plugin-react';

import sourcemaps from 'rollup-plugin-sourcemaps';

export default (env)=> ({
  // Array properties will concat on merge, so this will be added
  // to plugins, instead of overwriting
  plugins: [
  build: {
    sourcemap: true,
    rollupOptions: {
      plugins: [sourcemaps()],
      output: {
        strict: false,
        chunkFileNames: '[name]-[hash:10].js',
        manualChunks: {
          lodash: ['lodash'],
          react: ['react'],
          'react-dom': ['react-dom'],
          'react-router-dom': ['react-router-dom'],


See src/sbt-test/sbt-jsbundler for an example project. It includes a with further documentation.