Effects and async

Gova offers two hooks for side effects: UseEffect for arbitrary imperative work with cleanup, and UseAsync for one-shot loads whose result is bound to the view.

UseEffect

func UseEffect(s *Scope, fn func(ctx context.Context) func())

The callback runs once per mount. The context.Context is cancelled when the component unmounts. If the callback returns a non-nil function, that function runs on unmount.

func (v Clock) Body(s *gova.Scope) gova.View {
	now := gova.State(s, time.Now())
 
	gova.UseEffect(s, func(ctx context.Context) func() {
		ticker := time.NewTicker(time.Second)
		go func() {
			for {
				select {
				case <-ctx.Done():
					return
				case t := <-ticker.C:
					now.Set(t)
				}
			}
		}()
		return func() { ticker.Stop() }
	})
 
	return gova.Text(now.Format("time: %s"))
}

UseEffect is call-site keyed just like State, so the same effect is not rerun on every render; it is initialized once per mount.

UseAsync

func UseAsync[T any](s *Scope, fn func(ctx context.Context) (T, error)) (T, error, bool)

Runs the function in a goroutine and returns (data, err, loading). The first render returns the zero T, nil, and true. Once the goroutine finishes the state is updated and the component rerenders with the final (data, err, false) tuple.

The context is cancelled on unmount so the goroutine can exit cleanly.

func (v UserCard) Body(s *gova.Scope) gova.View {
	user, err, loading := gova.UseAsync(s, func(ctx context.Context) (User, error) {
		return fetchUser(ctx, v.UserID)
	})
 
	if loading {
		return gova.ProgressView()
	}
	if err != nil {
		return gova.Text(err.Error()).Color(gova.Destructive)
	}
	return gova.Text(user.Name).Font(gova.Title)
}

Like UseEffect, UseAsync is call-site keyed; the goroutine is started on first mount, not on every render.

Effects and async

UseEffect

UseAsync

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