Support dynamic data loading on UIElement mount

Hi everyone,

I’m trying to define, from JSON, that a component should call an external API when it mounts in order to populate its state, but I haven’t found a way to do it.

Could you please confirm whether this is currently supported, and if so, what the recommended approach would be?

For example:

{
  "root": "username",
  "elements": {
    "username": {
      "type": "Text",
      "props": { "content": { "$state": "/user/name" } },
      "children": []
    }
  },
  "state": {
    "user": undefined
  },
  "on": {
    "mount": [
      { "action": "fetchUser" }
    ]
  }
}

The idea is that fetchUser would internally perform a fetch request, retrieve the user data, and then update the component state accordingly.

Is this currently possible?
If not, is there an alternative or recommended pattern to achieve this behavior?

Start by tracing how UIElement mount events, JSON-defined actions, and component state updates are currently handled. Check whether an action such as fetchUser can perform asynchronous work and write returned data into state. Done should be a documented, working pattern—or a clearly stated limitation and recommended alternative for loading external data.