HeinrichApfelmus
commented
7 years ago The reason for this is garbage collection. The Haskell side tries to keep track of all Element in the DOM tree, and garbage collects them and their event handlers when they are no longer reachable. Tracking lifetimes for DOM elements is reasonably straightforward, in that they are usually only manipulated from the Haskell side, for instance by using getElementById or by using the children property.
This heuristic does not work for general JSObject (e.g. a JavaScript canvas object), because they can and will be manipulated by many different functions.
Note that it is common for an event handler to keep its element alive, which in turn keeps the handler alive, i.e. it is common that we have a circular reference. The only way to handle this properly is to use the Haskell garbage collector, because JavaScript garbage collector are impoverished.
What is your particular use case? I'm open to suggestion on how to incorporate more objects besides DOM elements.
pepeiborra
Threepenny exposes the events of JSObjects that correspond to DOM elements only. Is there a design reason for this ?
Currently all the primitives (fromJSObject, getEvents, addEvents) are private, as is the Window event vendor, so the only way to implement this properly from user land is to bolt a StateT on top of UI to carry a new event vendor.
If I'm missing something, please point me in the right direction.