Kotlin Wasm

With Kotlin, you have the power to build applications and reuse mobile and desktop user interfaces (UIs) in your web projects through Compose Multiplatform and Kotlin/Wasm.

Compose Multiplatform is a declarative framework based on Kotlin and Jetpack Compose that allows you to implement the UI once and share it across all the platforms you target. Specifically for web platforms, Compose Multiplatform uses Kotlin/Wasm as its compilation target.

Explore our online demo of an application built with Compose Multiplatform and Kotlin/Wasm

WebAssembly (Wasm) is a binary instruction format for a stack-based virtual machine. This format is platform-independent because it runs on its own virtual machine. Wasm provides Kotlin and other languages with a compilation target to run on the web.

Kotlin/Wasm compiles your Kotlin code into Wasm format. Using Kotlin/Wasm, you can create applications that run on different environments and devices, which support Wasm and meet Kotlin's requirements.

Additionally, you can use the most popular Kotlin libraries in Kotlin/Wasm out of the box. Like other Kotlin and Multiplatform projects, you can include dependency declarations in the build script. For more information, see Adding dependencies on multiplatform libraries.

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Kotlin/Wasm performance

Although Kotlin/Wasm is still in Alpha, Compose Multiplatform running on Kotlin/Wasm already shows encouraging performance traits. You can see that its execution speed outperforms JavaScript and is approaching that of the JVM:

We regularly run benchmarks on Kotlin/Wasm, and these results come from our testing in a recent version of Google Chrome.

Browser API support

The Kotlin/Wasm standard library provides declarations for browser APIs, including the DOM API. With these declarations, you can directly use the Kotlin API to access and utilize various browser functionalities. For example, in your Kotlin/Wasm applications, you can use manipulation with DOM elements or fetch the API without defining these declarations from scratch. To learn more, see our Kotlin/Wasm browser example.

The declarations for browser API support are defined using JavaScript interoperability capabilities. You can use the same capabilities to define your own declarations. In addition, Kotlin/Wasm–JavaScript interoperability allows you to use Kotlin code from JavaScript. For more information, see Use Kotlin code in JavaScript.

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