// Copyright 2018 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. //go:build js && wasm package js import "sync" var ( funcsMu sync.Mutex funcs = make(map[uint32]func(Value, []Value) any) nextFuncID uint32 = 1 ) // Func is a wrapped Go function to be called by JavaScript. type Func struct { Value // the JavaScript function that invokes the Go function id uint32 } // FuncOf returns a function to be used by JavaScript. // // The Go function fn is called with the value of JavaScript's "this" keyword and the // arguments of the invocation. The return value of the invocation is // the result of the Go function mapped back to JavaScript according to ValueOf. // // Invoking the wrapped Go function from JavaScript will // pause the event loop and spawn a new goroutine. // Other wrapped functions which are triggered during a call from Go to JavaScript // get executed on the same goroutine. // // As a consequence, if one wrapped function blocks, JavaScript's event loop // is blocked until that function returns. Hence, calling any async JavaScript // API, which requires the event loop, like fetch (http.Client), will cause an // immediate deadlock. Therefore a blocking function should explicitly start a // new goroutine. // // Func.Release must be called to free up resources when the function will not be invoked any more. func FuncOf(fn func(this Value, args []Value) any) Func { funcsMu.Lock() id := nextFuncID nextFuncID++ funcs[id] = fn funcsMu.Unlock() return Func{ id: id, Value: jsGo.Call("_makeFuncWrapper", id), } } // Release frees up resources allocated for the function. // The function must not be invoked after calling Release. // It is allowed to call Release while the function is still running. func (c Func) Release() { funcsMu.Lock() delete(funcs, c.id) funcsMu.Unlock() } // setEventHandler is defined in the runtime package. func setEventHandler(fn func() bool) func init() { setEventHandler(handleEvent) } // handleEvent retrieves the pending event (window._pendingEvent) and calls the js.Func on it. // It returns true if an event was handled. func handleEvent() bool { // Retrieve the event from js cb := jsGo.Get("_pendingEvent") if cb.IsNull() { return false } jsGo.Set("_pendingEvent", Null()) id := uint32(cb.Get("id").Int()) if id == 0 { // zero indicates deadlock select {} } // Retrieve the associated js.Func funcsMu.Lock() f, ok := funcs[id] funcsMu.Unlock() if !ok { Global().Get("console").Call("error", "call to released function") return true } // Call the js.Func with arguments this := cb.Get("this") argsObj := cb.Get("args") args := make([]Value, argsObj.Length()) for i := range args { args[i] = argsObj.Index(i) } result := f(this, args) // Return the result to js cb.Set("result", result) return true }