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WASM Island ABI

This example shows the supported component-level WASM island package shape.

component WasmCounter
wasm ./examples/components/wasm/browser/counter

The browser Go package is a normal package main compiled with GOOS=js GOARCH=wasm. It must export the component-scoped ABI functions with //go:wasmexport:

import gowdkwasm "github.com/cssbruno/gowdk/runtime/wasm"

//go:wasmexport GOWDKMountWasmCounter
func GOWDKMountWasmCounter() uint32 {
	return gowdkwasm.ReturnResult(gowdkwasm.Result{Patches: []any{}})
}

Build It

Run from the repository root:

go run ./cmd/gowdk build --out /tmp/gowdk-wasm-island examples/components/wasm/*.gwdk
test -f /tmp/gowdk-wasm-island/components/wasm/index.html
test -f /tmp/gowdk-wasm-island/assets/gowdk/islands/componentwasm/WasmCounter.wasm
test -f /tmp/gowdk-wasm-island/assets/gowdk/islands/componentwasm/WasmCounter.wasm.js
test -f /tmp/gowdk-wasm-island/assets/gowdk/islands/wasm_exec.js

The current ABI validates required exports and browser-safe imports, emits the host loader, decodes Go-style uint32 JSON result pointers, and reports unsupported patch operations in the browser console. Use runtime/wasm to read the current mount/event/destroy payload and return either a legacy patch array or the extended { "patches": [...], "stores": { ... } } result shape.

Page stores

A WASM island that declares use <store> in its client block participates in page stores like a JS island. The host loader:

  • reads every used store and merges its current (and persisted) value into the state field of the mount/handle/destroy payload, and passes the used store names in payload.stores;
  • writes back when an export returns the extended result shape { "patches": [...], "stores": { "<name>": <value> } } — each returned store value is written to window.__gowdkStores. The legacy bare patch array is still accepted (no store write-back);
  • syncs on external changes: when another island updates a used store, the loader re-invokes the mount export with the refreshed state and applies the returned patches, without echoing the update back into the registry.

Surfacing serialized state from the uint32 export contract (so a Go island can return the stores map) is implemented by the runtime/wasm helper and host loader pointer decoding.