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Head-to-head · Code Transpilers

Kotlin/JS vs Scala.js

  • Updated Oct 2026
  • Both researched from official sources
  • 5 checks side by side
Higher score Kotlin/JS #3 in Code Transpilers 8.8/10 Free plan Free plan✓ 3 of 4 features Visit Kotlin/JS
Scala.js #8 in Code Transpilers 8.3/10 Open source ✓ 3 of 4 features Visit Scala.js

Kotlin/JS leads on 0 checks, Scala.js on 0, and 5 are even. Who comes out ahead on the 5 yes/no, price and count checks where we have data for both products. The editor score weighs everything else too.

Our verdict

  • Highest scoreKotlin/JS · 8.8/10
  • Free planonly Kotlin/JS

Kotlin/JS scores higher on our rubric for code transpilers: 8.8 against 8.3 out of 10; our editors rank them #3 and #8.

On conversion mode, Scala.js gives you Both where Kotlin/JS offers Source-to-source.

Kotlin/JS is the better fit for kotlin teams targeting browsers or Node.js. Scala.js is the better fit for scala teams building JavaScript applications.

  • Kotlin/JS fits best

    Kotlin teams targeting browsers or Node.js

  • Scala.js fits best

    Scala teams building JavaScript applications

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Side by side

Feature Kotlin/JS 8.8/10 Visit ↗ Scala.js 8.3/10 Visit ↗
At a glance
Editor score 8.8 8.3
Ranking #3 in Code Transpilers #8 in Code Transpilers
Best for Kotlin teams targeting browsers or Node.js Scala teams building JavaScript applications
Pricing model Free Free
Starting price Free plan Open source
Free plan ✓ (best) Not checked yet
Free trial — —
Deployment Self-hosted Self-hosted
Support Community, Docs Community, Docs
Integrations 6 integrations 5 integrations
Built for Solo, Small business, Mid-market, Enterprise Solo, Small business, Mid-market, Enterprise
Features Kotlin/JS 3/4 · Scala.js 3/4
Syntax-version conversion ✓ (best) Not checked yet
Intermediate output ✓ ✓
CLI access ✓ ✓
API access Not checked yet ✓ (best)
Specs
Source languages Not checked yet Not checked yet
Target languages Not checked yet Not checked yet
Conversion mode Source-to-source Both
Our review
Pros
  • Compiles to ES5 and ES2015 for browser and Node.js targets
  • Supports npm packages, webpack, and JavaScript module interoperability
  • Generates TypeScript declarations and offers production minification
  • Incremental compilation supports iterative Scala-to-JavaScript builds
  • Dead-code elimination and linking help shape JavaScript output
  • Interop includes JavaScript libraries, React, AngularJS, Node.js, and Vite
Cons
  • Requires Kotlin code and compatible dependencies as input
  • Projects are configured through the Kotlin Multiplatform Gradle plugin
  • Support channels are community resources and documentation
  • Requires Scala source code, so it is not a general-purpose transpiler
  • Project workflows are commonly managed through build tools such as sbt
  • Support is through community channels and documentation
Our verdict

Kotlin/JS is a source-to-source compiler and development toolchain for building browser and Node.js applications with Kotlin. It transpiles Kotlin code, the standard library, and compatible dependencies into JavaScript, with ES5 and ES2015…

Read the review →

Scala.js brings Scala into JavaScript application development by compiling Scala source files into JavaScript. It is aimed at teams that want to write application logic in Scala while targeting browsers, Node.js, or JavaScript modules. The…

Read the review →
  1. Kotlin/JSCode Transpilers 8.8Free plan
  2. Scala.jsCode Transpilers 8.3Open source

Strengths and trade-offs

  • Kotlin/JS — where it wins

    • Compiles to ES5 and ES2015 for browser and Node.js targets
    • Supports npm packages, webpack, and JavaScript module interoperability
    • Generates TypeScript declarations and offers production minification

    Where it doesn't

    • Requires Kotlin code and compatible dependencies as input
    • Projects are configured through the Kotlin Multiplatform Gradle plugin
    • Support channels are community resources and documentation

  • Scala.js — where it wins

    • Incremental compilation supports iterative Scala-to-JavaScript builds
    • Dead-code elimination and linking help shape JavaScript output
    • Interop includes JavaScript libraries, React, AngularJS, Node.js, and Vite

    Where it doesn't

    • Requires Scala source code, so it is not a general-purpose transpiler
    • Project workflows are commonly managed through build tools such as sbt
    • Support is through community channels and documentation

More comparisons

All code transpilers comparisons → · Full ranking →

Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

Last updated · How we research and update