As previously guided in our API updates for July 2018, if event handlers are registered asynchronously for the below events, a warning will be displayed in the browser console.
- Record Details Event : app.record.detail.show
- Record Create Event : app.record.create.show
- Record Edit Event : app.record.edit.show
The warning contains a link to the "Best practices for registering event handlers" article.
Be sure to check this article out if you are working with JavaScript customization on Kintone.