Module `Incr_dom.Component`

A Component captures the basic operations that need to be provided in order to build an Incr_dom app. The same type can be used both at the top-level of an app, as well as for defining individual components within a larger app.

The Component.t is often constructed incrementally, and is always created incrementally at the top-level, as is required by App_intf.S.

type ('action, 'model, 'state, 'extra) with_extra: The with_extra type allows the component to expose extra information that might be useful to the user of the component. This allows the module in which the component is defined to expose functions that can be used to query incrementally computed information about the the component.

type ('action, 'model, 'state) t = ('action, 'model, 'state, unit) with_extra

val apply_action : ('action, 'model, 'state, _) with_extra -> 'action -> 'state -> schedule_action:('action -> unit) -> 'model: apply_action is called to update the model in response to the arrival of a scheduled action. The function may have side effects, which among other things can trigger more actions.

val update_visibility : ('action, 'model, _, _) with_extra -> schedule_action:('action -> unit) -> 'model

update_visibility is called in order to allow the component to query the state of the DOM to determine what is currently in view, and put that information into the model. This in turn allows for the rendering to limit the set of DOM nodes actually created to those that are in sight.

Start_app calls update_visibility when a top-level resize or scroll is detected. Also, individual components that create scrollable widgets should create DOM event handlers that return the Viewport_changed event from Virtual_dom.Vdom.Event when those widgets are scrolled or resized. Otherwise, visibility changes may not be correctly captured.

Note that changes in visibility could trigger changes to the DOM that in turn cause the page to reflow. This can cause more changes in visibility, which can lead to an infinite loop. Such behavior is a bug in the component, but the framework doesn't attempt to stop cascading sequences of update_visibility, so that these bugs are not hidden.

val view : (_, _, _, _) with_extra -> Virtual_dom.Vdom.Node.t: view is called to obtain the virtual DOM which is then applied to the actual DOM.

val extra : (_, _, _, 'extra) with_extra -> 'extra: extra allows you to expose extra information that was derived from the model. Note that for most components, extra has type unit.

val on_display : ('action, _, 'state, _) with_extra -> 'state -> schedule_action:('action -> unit) -> unit: on_display is called every time the DOM is updated, with the model just before the update and the model just after the update. Use on_display to initiate actions.

val create : ?⁠apply_action:('action -> 'state -> schedule_action:('action -> unit) -> 'model) -> ?⁠update_visibility:(schedule_action:('action -> unit) -> 'model) -> ?⁠on_display:('state -> schedule_action:('action -> unit) -> unit) -> 'model -> Virtual_dom.Vdom.Node.t -> ('action, 'model, 'state) t

Though this create function is not incremental, it is usually called in the context of an incremental computation function, like the one in App_intf.S. If some arguments are not supplied, defaults (which either return the model supplied or unit) are included in the component.

Note that the functions apply_action, update_visibility and on_display are allowed to perform effects, but the incremental computation that produces create should itself be functional.

val create_with_extra : ?⁠apply_action:('action -> 'state -> schedule_action:('action -> unit) -> 'model) -> ?⁠update_visibility:(schedule_action:('action -> unit) -> 'model) -> ?⁠on_display:('state -> schedule_action:('action -> unit) -> unit) -> extra:'extra -> 'model -> Virtual_dom.Vdom.Node.t -> ('action, 'model, 'state, 'extra) with_extra: Like create, but allows for the specification of the extra parameter, which allows for component-specific state to be exposed.