sbt-splice · v0.3.2

Overview

You do not install Node, Vite, or esbuild. spliceFull is the production bundle Scala.js 1.21 asked you to get from Vite: type-aware Scala minify, then a general JS minifier that leaves protocol names (render, setState) and class extends Error alone. The minifier is a pinned esbuild binary. First spliceFull fetches it through Coursier for this OS/arch, checks sha256, and runs it. A clone of the project is enough. JDK and sbt were already required.

Scala.js lets you write import "preact" from Scala, usually with @JSImport("preact") (or require for CommonJS). The linker then emits a JavaScript file that still says import "preact". A browser cannot resolve that name. There is no node_modules folder, and the browser does not ask npm what "preact" means. The leftover name is a specifier. sbt-splice points each specifier at pinned bytes (a file in the repo, a WebJar, or a CDN/GitHub download with sha256) and writes one JavaScript file for a <script> tag.

If the program has no npm imports, leave spliceLibs empty. spliceFull is still the production file. NoModule is the natural linker kind in that case.

Fast vs full

spliceFast bundles the linker's own imports and stops there (development, NODE_ENV is "development"). spliceFull is that same bundle, minified (NODE_ENV is "production"). Source maps are on for fast and off for full and closure unless you turn them on. Empty spliceLibs stays a classic script, not an iife, and spliceFull still minifies it. spliceClosure is optional Closure advanced on Scala.js's output; unused library exports stay on that path. Vanilla fastLinkJS / fullLinkJS are unchanged. Splice writes target/splice/fast.js, target/splice/full.js, and target/splice/closure.js.

List(
  "spliceFast"    -> "bundle the linker's imports (development)",
  "spliceFull"    -> "bundle and minify (production)",
  "spliceClosure" -> "Closure on Scala.js; libraries are not shaken",
)
List((spliceFast,bundle the linker's imports (development)), (spliceFull,bundle and minify (production)), (spliceClosure,Closure on Scala.js; libraries are not shaken))

If you already use Vite

You can drop Node from the Scala.js production path. Vite's minify leaves JS property names alone and keeps class / super(). So does spliceFull. esbuild also drops the ESM exports the linked program does not use, including an import * as when the program only reads some properties. Passing that module on as a value keeps them. Top-level side effects stay. An export * as inside a pinned file is not shaken (esbuild's limit). CommonJS is not promised to shrink. A library the linker never imports is absent. Splice does not walk node_modules, does not read package.json, does not run npm, and does not leave import "preact" for another bundler to fix. Libraries are sealed pins. The output is one <script> file.

How that compares to Closure, and why property renaming stays off, is on Production minify.