Kotlin Help


Kotlin/Wasm relies on new WebAssembly proposals like garbage collection and exception handling to introduce improvements and new features within WebAssembly.

However, to ensure these features work properly, you need an environment that supports the new proposals. In some cases, you may need to set up the environment to make it compatible with the proposals.

Browser versions

To run applications built with Kotlin/Wasm in a browser, you need a browser version supporting the new WebAssembly garbage collection (WasmGC) feature. Check if the browser version supports the new WasmGC by default or if you need to make changes to the environment.


  • For version 119 or later:

    Works by default.

  • For older versions:

    1. In your browser, go to chrome://flags/#enable-webassembly-garbage-collection.

    2. Enable WebAssembly Garbage Collection.

    3. Relaunch your browser.


Including Chromium-based browsers such as Edge, Brave, Opera, or Samsung Internet.

  • For version 119 or later:

    Works by default.

  • For older versions:

    Run the application with the --js-flags=--experimental-wasm-gc command line argument.


  • For version 120 or later:

    Works by default.

  • For version 119:

    1. In your browser, go to about:config.

    2. Enable javascript.options.wasm_gc option.

    3. Refresh the page.


WebAssembly garbage collection support is currently under active development.

Wasm proposals support

Kotlin/Wasm improvements are based on WebAssembly proposals. Here you can find details about the support for WebAssembly's garbage collection and exception handling proposals.

Garbage collection proposal

Since Kotlin 1.9.20, the Kotlin toolchain uses the latest version of the Wasm garbage collection (WasmGC) proposal.

For this reason, we strongly recommend that you update your Wasm projects to the latest version of Kotlin. We also recommend you use the latest versions of browsers with the Wasm environment.

Exception handling proposal

Since Kotlin 2.0.0, we have introduced support for the new version of Wasm exception handling proposal within Kotlin/Wasm.

This update ensures the new exception handling proposal aligns with Kotlin requirements, enabling the use of Kotlin/Wasm on virtual machines that only support the latest version of the proposal.

The new exception handling proposal is activated using the -Xwasm-use-new-exception-proposal compiler option. It is turned off by default.


Last modified: 21 May 2024