When an ajax action (using submitlink, [ajax] attribute or when already in ajax context) fails due to a server error (such as “could not dispatch to a proper action”, because the action is no longer available), display an error to the user.
An update to common_.css will place the error message in a full-width bar at the bottom of the page (dismissible). The default message will be:

Error while handling this action, the server returned status 503/404/…. The action may no longer be available. Copy your unsaved changes before leaving/refreshing this page.

This failure message can be customized by:

• setting a page-specific action failure message
  • by using actionFailureMessage( "Error while processing this action, ..." ) (builtin.app)
  • by setting js var window.actionFailureMessage directly
• setting an action-element (button, submitlink) specific message using attribute data-action-failed, e.g. submitlink save()[data-action-failed="Could not save your answer. Copy your unsaved changes before refreshing/leaving this page."]

Submitted by Elmer van Chastelet on 15 March 2019 at 10:50