promise

func New ¶

func New(rt *sobek.Runtime, async func(callback Callback)) sobek.Value

New creates a sobek.Promise that wraps an asynchronous operation. The async function runs in a separate goroutine and can safely interact with JavaScript values through the provided callback. The callback ensures all JavaScript operations happen on the main goroutine.

The callback return:

• result (any): The value to resolve the promise with
• error: If non-nil, the promise will be rejected with this error

If a panic occurs in either the async function or callback, the promise will be rejected with the panic value.

Example usage - implementing an async fetch function:

func main() {
	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		_, _ = w.Write([]byte(`{"foo":"bar"}`))
	}))
	defer server.Close()

	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	defer cancel()

	fetch := func(call sobek.FunctionCall, rt *sobek.Runtime) sobek.Value {
		return promise.New(rt, func(callback promise.Callback) {
			res, err := http.Get(call.Argument(0).String())
			callback(func() (any, error) {
				if err != nil {
					return nil, err
				}
				defer res.Body.Close()
				data, err := io.ReadAll(res.Body)
				if err != nil {
					return nil, err
				}
				return string(data), nil
			})
		})
	}

	var (
		value sobek.Value
		err   error
	)
	err = js.Run(ctx, func(rt *sobek.Runtime) error {
		_ = rt.Set("fetch", fetch)
		value, err = rt.RunString(fmt.Sprintf(`fetch("%s")`, server.URL))
		return err
	})
	if err != nil {
		panic(err)
	}
	fmt.Println(value.Export().(*sobek.Promise).Result().Export())
}

func Reject ¶

func Reject(rt *sobek.Runtime, reason any) sobek.Value

Reject with reason

func Resolve ¶

func Resolve(rt *sobek.Runtime, value any) sobek.Value

Resolve with value

func Result ¶

func Result(value sobek.Value) (any, error)

Result returns the promise result, if it not promise return origin value.