feat: Implement Promise.await()

wasm/promise.go

@@ -15,6 +15,42 @@ func (p *Promise) FromJSValue(value js.Value) error {
 	return err
 }
 
+// Await waits for the promise to be fulfilled or rejected.
+// It returns an error if there was an error unmarshalling or interacting with JS.
+//
+// This function returns true and sets the value of 'out' if the promise is fulfilled.
+// It returns false and sets the value of 'rej' if the promise is rejected.
+func (p Promise) Await(out, rej interface{}) (bool, error) {
+	resultChan := make(chan js.Value)
+	errChan := make(chan js.Value)
+
+	next, err := p.Get("next")
+	if err != nil {
+		return false, err
+	}
+
+	catch, err := p.Get("catch")
+	if err != nil {
+		return false, err
+	}
+
+	next.Invoke(ToJSValue(func(_, result js.Value) js.Value {
+		resultChan <- result
+		return result
+	}))
+	catch.Invoke(ToJSValue(func(_, err js.Value) js.Value {
+		errChan <- err
+		return err
+	}))
+
+	select {
+	case jsOut := <-resultChan:
+		return true, FromJSValue(jsOut, out)
+	case jsErr := <-errChan:
+		return false, FromJSValue(jsErr, rej)
+	}
+}
+
 // NewPromise returns a promise that is fulfilled or rejected when the provided handler returns.
 // The handler is spawned in its own goroutine.
 func NewPromise(handler func() (interface{}, error)) Promise {