https://lynxjs.org/api/elements/built-in/text.html#layout

The layout event returns the result information after text layout, including the number of lines of the current text, and the start and end positions of the text in each line relative to the entire text.

data Action = HandleLayout LayoutEvent

view :: Model -> View Action
view model = text_ [ onLayout HandleLayout ] [ text "hi" ]

update :: Action -> Effect Model Action
update (HandleLayout LayoutEvent {..}) = io_ (consoleLog "layout event received")

https://lynxjs.org/api/elements/built-in/text.html#selectionchange

This event is triggered whenever the selected text range changes.

data Action = HandleSelectionChange SelectionChangeEvent

view :: Model -> View Action
view model = text_ [ onSelectionChange HandleSelectionChange ] [ text "hi" ]

update :: Action -> Effect Model Action
update (HandleSelectionChange SelectionChangeEvent {..}) =
  io_ (consoleLog "selection change event received")