GX4013: optimistic directive has no action or writes no signal

Cause#

An optimistic:<event> directive changes signals before the request of an action. When the action fails, the runtime puts the values of before back.

The directive needs two things:

• An on:<event> handler on the same element, for the same event, that invokes an action. Without it, there is no request that can fail.
• A statement that writes a signal of the component. The runtime saves only the signals that the statements write.

Example#

package route

import "github.com/alternayte/gx"

type Like struct {
	gx.Route `POST /likes/like`
}

package likes

import (
	"github.com/alternayte/gx"
	"app/likes/route"
)

var like = gx.Action(func(c *gx.Ctx, in route.Like) error {
	return nil
})

var Routes = gx.Collect(like)

package likes

signals {
  Count int = 0
}

<div>
  <span text={$Count}></span>
  <button optimistic:click={$Count++}>Like</button>
</div>

gx check reports:

likes/Likes.gx:9:11: GX4013: optimistic directive: the element has no on:click handler that invokes an action

Fix#

1. Add the action to the element: <button on:click={route.Like{}} optimistic:click={$Count++}>.
2. Use the same event in the two directives.
3. For a change with no request, use on:click={$Count++}.