feat(wasm): add CreateWasmFuncWithReturn for value-returning JS callbacks

cmd/version.go

@@ -9,7 +9,7 @@ import (
 	"github.com/spf13/cobra"
 )
 
-var CURRENT_VERSION string = "v2.17.3"
+var CURRENT_VERSION string = "v2.17.4"
 
 // versionCmd represents the version command
 var versionCmd = &cobra.Command{

pkg/wasm/stubs.go

@@ -204,6 +204,22 @@ func CreateWasmFunc(name string, fn func())            {}
 func CreateWasmStringFunc(name string, fn func(string)) {}
 func CreateWasmBoolFunc(name string, fn func(bool))    {}
 
+// CreateWasmFuncWithReturn registers a named global JS function that can return a value back to JS.
+// Wraps syscall/js.FuncOf. Use when a JS library expects a callback that returns a value
+// synchronously (e.g. option objects, formatters, renderers). The function persists for the
+// lifetime of the page. Returns a JSValue so it can be passed directly to JS object properties.
+//
+// Example:
+//
+//	// Register a callback and pass it as a property on a JS config object:
+//	cb := CreateWasmFuncWithReturn("myCallback", func(this JSValue, args []JSValue) any {
+//	    return args[0].String() + "_suffix"
+//	})
+//	config.Set("formatter", cb)
+func CreateWasmFuncWithReturn(name string, fn func(this JSValue, args []JSValue) any) JSValue {
+	return JSValue{}
+}
+
 // ── Topic infrastructure (generated code only — not part of the user API) ────
 
 // TopicKey is a typed key used by the auto-generated topic system.

pkg/wasm/wasm-runtime/runtime/events.go

@@ -205,3 +205,21 @@ func CreateWasmBoolFunc(name string, fn func(bool)) {
 		})
 	})
 }
+
+// CreateWasmFuncWithReturn registers a named global JS function that can return a value back to JS.
+// Wraps syscall/js.FuncOf. The returned JSValue holds the js.Func so it can be passed
+// directly to JS object properties (chart configs, map renderers, etc.) that require a
+// synchronous return value. The js.Func is retained in keep and never released — it must
+// stay alive for the lifetime of the page; releasing it would panic on the next invocation.
+func CreateWasmFuncWithReturn(name string, fn func(this JSValue, args []JSValue) any) JSValue {
+	f := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+		jsArgs := make([]JSValue, len(args))
+		for i, a := range args {
+			jsArgs[i] = JSValue{a}
+		}
+		return toJSVal(fn(JSValue{this}, jsArgs))
+	})
+	keep = append(keep, f)
+	js.Global().Set(name, f)
+	return JSValue{f.Value}
+}

pkg/wasm/wasm-runtime/runtime/events_stub.go

@@ -5,3 +5,5 @@ package runtime
 func CreateWasmFunc(name string, fn func())            {}
 func CreateWasmStringFunc(name string, fn func(string)) {}
 func CreateWasmBoolFunc(name string, fn func(bool))    {}
+
+func CreateWasmFuncWithReturn(name string, fn func(this JSValue, args []JSValue) any) JSValue { return JSValue{} }