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Scala.js

Scala.js is a Scala-to-JavaScript compiler for applications that run in browsers, Node.js, and serverless environments.

Place
#13 of 28
Score
6.3
Scala.js's website

What Scala.js is

Scala.js is a Scala-to-JavaScript compiler for applications that run in browsers, Node.js, and serverless environments. It also has stable WebAssembly support. Its strong typing can help catch errors such as mixing strings and numbers or calling a misspelled method. Editor support can flag type errors and typos, with inline information about methods, arguments, return types, and documentation. The project describes incremental compilation with a 1–2 second turnaround; generated JavaScript for a full application starts at 45 kB gzipped. Scala.js can use JavaScript libraries and APIs through either statically or dynamically typed access. Listed integrations include React, Angular, Vue, Three.js, and Chart.js. Build options include sbt, scala-cli, Mill, and Gradle with a Scala.js plugin. Tutorials list Scala development tools and Node.js as prerequisites and recommend VS Code with Metals. Scala.js is free and open source under the Apache License Version 2.0, with community help available through Discord and Stack Overflow. The 1.22.0 release is not entirely backward source compatible with 1.21.x.

Good

  • Supports browser, Node.js, serverless, and WebAssembly targets
  • Strong typing helps catch common mistakes
  • Offers static and dynamic JavaScript access
  • Supports several Scala build tools
  • Free and open source

Watch out

  • Requires Scala development tools and Node.js
  • 1.22.0 is not fully source-compatible with 1.21.x

Who it suits

Scala developers building browser, Node.js, serverless, or WebAssembly applications may find it suitable. It may also suit teams that want to use JavaScript libraries while working with Scala.

Verdict

Scala.js brings Scala's type checking and tooling to JavaScript applications, with routes to several common build tools and libraries. Check the 1.21.x compatibility note before upgrading to 1.22.0.

Plans and prices

From Scala.js's own pricing page, checked 4 Oct 2026.

All about pricing
PlanPriceWhat it gives you
Scala.jsFreeScala to JavaScript compiler · managed through a Scala build tool

The facts

Each one read from Scala.js's own pages, with the date it was checked.

What it does

Build tools
The documentation names sbt, scala-cli, Mill, and Gradle with a Scala.js plugin as supported build tool options.checked 4 Oct 2026
Compatibility note
The 1.22.0 release announcement says the release is not entirely backward source compatible with 1.21.x.checked 4 Oct 2026
Correctness
The site says Scala.js uses strong typing to catch mistakes such as mixing strings and numbers or calling methods with typos.checked 4 Oct 2026
Development setup
The tutorials list Scala development tools and Node.js as prerequisites and recommend VS Code with the Metals extension.checked 4 Oct 2026
Editor support
The homepage says editor support catches typos and type errors and provides inline method, argument, return type, and documentation information.checked 4 Oct 2026
JavaScript interoperability
Scala.js can use JavaScript libraries and interact with JavaScript APIs, with either statically or dynamically typed access.checked 4 Oct 2026
Library ecosystem
The libraries page lists facades and integrations for libraries including React, Angular, Vue, Three.js, and Chart.js.checked 4 Oct 2026
License
The project repository states that Scala.js is distributed under the Apache License Version 2.0.checked 4 Oct 2026
Output targets
The June 2026 release announcement says WebAssembly support is stable; the homepage describes browser, Node.js, and serverless apps.checked 4 Oct 2026
Performance
The site describes incremental compilation with 1–2 second turnaround and generated JavaScript starting at 45 kB gzipped for a full application.checked 4 Oct 2026
Purpose
Scala.js is a Scala to JavaScript compiler for building applications that run in browsers, Node.js, and serverless environments.checked 4 Oct 2026
Support
The documentation directs users to the community for help, including Discord and Stack Overflow.checked 4 Oct 2026

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