Function NewJSInterface

client/wasm/internal/websocket/websocket.go:160–215

NewJSInterface creates a JavaScript object wrapping the WebSocket connection. It exposes: send(string|Uint8Array), close(), and callback properties onmessage, onclose, onerror. Callback properties may be set from the JS thread while the read loop goroutine reads them. In WASM this is safe because G

(conn *Conn)

// single thread, but the design would need synchronization on
// multi-threaded runtimes.
func NewJSInterface(conn *Conn) js.Value {
	obj := js.Global().Get("Object").Call("create", js.Null())

	sendFunc := js.FuncOf(func(_ js.Value, args []js.Value) any {
		if len(args) < 1 {
			log.Errorf("websocket send requires a data argument")
			return js.ValueOf(false)
		}

		data := args[0]
		switch data.Type() {
		case js.TypeString:
			if err := conn.WriteText([]byte(data.String())); err != nil {
				log.Errorf("failed to send websocket text: %v", err)
				return js.ValueOf(false)
			}
		default:
			buf, err := jsToBytes(data)
			if err != nil {
				log.Errorf("failed to convert js value to bytes: %v", err)
				return js.ValueOf(false)
			}
			if err := conn.WriteBinary(buf); err != nil {
				log.Errorf("failed to send websocket binary: %v", err)
				return js.ValueOf(false)
			}
		}
		return js.ValueOf(true)
	})
	obj.Set("send", sendFunc)

	closeFunc := js.FuncOf(func(_ js.Value, _ []js.Value) any {
		if err := conn.Close(); err != nil {
			log.Debugf("failed to close websocket: %v", err)
		}
		return js.Undefined()
	})
	obj.Set("close", closeFunc)

	go func() {
		defer func() {
			if err := conn.Close(); err != nil && !errors.Is(err, net.ErrClosed) {
				log.Debugf("close websocket on readLoop exit: %v", err)
			}
		}()
		readLoop(conn, obj)
		// Undefining before Release turns post-close JS calls into TypeError
		// instead of a silent "call to released function".
		obj.Set("send", js.Undefined())
		obj.Set("close", js.Undefined())
		sendFunc.Release()
		closeFunc.Release()
	}()

	return obj
}

func jsToBytes(data js.Value) ([]byte, error) {