Kotlin Expands Horizons: Support for a New Platform in Multiplatform Development

Kotlin Now Supports a New Platform: What Does This Mean for Developers?

The JetBrains team continues to actively develop the Kotlin ecosystem, making it one of the most flexible and modern in the programming world. In the latest release, developers announced support for a new platform — WebAssembly (Wasm) in the Stable stage. This is a key event for everyone who uses Kotlin Multiplatform (KMP) and strives to write code once, running it everywhere: from servers and mobile devices to browsers and edge devices.

Why WebAssembly?

WebAssembly is a low-level binary format that runs in the browser at near-native speed. Previously, Kotlin already supported compilation to JavaScript, but Wasm opens up new possibilities:

• Performance: Kotlin code compiled to Wasm runs 1.5–2 times faster than a similar JS bundle, especially in computationally intensive tasks (graphics, data processing, games).
• Security: Wasm runs in an isolated sandbox, reducing the risk of vulnerabilities.
• Versatility: Wasm is supported by all modern browsers (Chrome, Firefox, Safari, Edge), as well as server environments (WASI) and IoT devices.

How Does It Work?

Now in Kotlin projects, you can specify the wasmJs or wasmWasi target in the build.gradle.kts file:

kotlin {    wasmJs {        browser { }    }    wasmWasi {        nodejs { }    }}

After compilation, you get a .wasm file that can be embedded in an HTML page or run in an environment that supports WASI. Important: the standard Kotlin/Wasm library, which is fully compatible with Kotlin/JS, is used for working with the DOM and browser APIs.

What Does This Give Developers?

• Unified stack for web and native: Now you can write business logic in Kotlin and reuse it between Android, iOS, the server (JVM), and the web client (Wasm).
• Quick project start: No need to learn TypeScript or Rust for high-performance web — just knowing Kotlin is enough.
• Simplified DevOps: One language, one build system (Gradle), and one codebase for all platforms.

Usage Example

Imagine you are writing a library for working with large JSON files. With Wasm, it will run in the browser without the delays typical of JavaScript. Additionally, Kotlin/Wasm supports coroutines and serialization (kotlinx.serialization), making the code concise and safe.

When to Try It?

Wasm support is already available in Kotlin 2.1.0 and higher. JetBrains recommends starting small: migrate modules not related to the UI (API clients, validators, encryption) to Wasm. Over time, full support for Compose Multiplatform for Wasm is planned, which will allow creating full-fledged web applications in Kotlin.

Conclusion

Adding WebAssembly to the list of supported platforms is not just another update. It is a step towards making Kotlin the number one language for multiplatform development. Now you have a tool that combines the performance of native code with the versatility