Learn KOTLIN-JS-WASM with Real Code Examples

Kotlin/JS compiles Kotlin code into JavaScript or WebAssembly.

Wasm backend (Kotlin/Wasm) provides near-native performance and small binaries.

Highly interoperable with JavaScript through Kotlin’s JS/interop APIs.

Integrated with Kotlin Multiplatform to share logic across JS, JVM, Android, and Native.

Designed for modern browser apps, UI frameworks, and high-performance computations.

Kotlin -> JS/Wasm compiler via Kotlin IR backend

Full type-safety across browser and JS ecosystem

Seamless DOM and Web API interoperability

Wasm-GC support enabling efficient managed memory

Multiplatform project architecture

Kotlin/JS -> transpiles Kotlin IR to JavaScript

Kotlin/Wasm -> compiles Kotlin IR to WebAssembly (.wasm)

Interop -> JS functions and DOM bindings via Kotlin

Multiplatform -> shared Kotlin code across targets

Compose for Web -> declarative UI on JS/Wasm

shared/ - shared Kotlin module

jsApp/ - Kotlin/JS or Kotlin/Wasm app

build.gradle.kts - configuration

src/jsMain/kotlin - browser code

dist/ - generated Wasm/JS bundles

Write Kotlin shared + JS/Wasm modules

Configure Gradle targets

Run dev server or compile to Wasm/JS

Interact with DOM via Kotlin APIs

Bundle output for deployment

Beginner: simple DOM manipulation

Intermediate: Kotlin + JS library interop

Advanced: Compose for Web UI

Expert: Kotlin/Wasm optimization + GC tuning

Auditor: analyzing Wasm binary + performance

Kotlin/Wasm vs TypeScript: stronger type safety & multiplatform

Kotlin/JS vs React/TS: similar, but Kotlin has safer typing

Kotlin/Wasm vs Rust/Wasm: easier language, slightly slower

Kotlin/Wasm vs Go/TinyGo: better tooling, larger runtime

Kotlin/Wasm vs SwiftWasm: similar, Kotlin more mature for web

2019 – Kotlin/JS IR introduced

2022 – Kotlin/Wasm experimental

2023 – Wasm-GC integrated

2024 – Compose for Web stable

2025 – Kotlin/Wasm widely adopted in production

IR - Intermediate Representation backend

Interop - JS <-> Kotlin connection

Wasm-GC - Managed memory Wasm runtime

Compose for Web - Kotlin UI DSL

Multiplatform - shared code across JVM/JS/Wasm