Callback option for t.modal() opened from iframe

Trello
1

I have discovered an unexpected issue.

It appears that in secondary iframes the callback for t.modal() (I noticed this for t.boardBar() as well) is not called.

t= window.TrelloPowerUp.iframe();
t.modal({
   title: "Title",
   url: 'http://myurl.com',
   fullscreen: true,
   callback: () => {
        // never gets here!!!!
         debugger;
         show();
     }
 });

The callback function is never called. The callback is called if I open modal using “t” passed to me by Trello.

I would really appreciate your help with this. Not being able to know when a dialog is closed creates an unpleasant UI problem.

Thank you in advance,
Boris

2

Great question that has taken a fair bit of debugging.

The short answer is, this happens because the secondary iframe that opens the modal is destroyed when the modal is opened and so we lose access to the callbacks it is holding onto. Unfortunately, there isn’t a quick and easy solution to make it “just work.” I’d recommend moving the responsibility of doing whatever the callback did to the modal itself and letting it perform the callback when its time to cleanup.

The long answer requires explaining a bit about how callbacks work. When you call t.modal() from the secondary iframe and pass along a function for the callback, the client library let’s the Trello web client know that there is a callback, and the web client responds and tells the iframe, “hold onto that callback function until I tell you to let it go.” So the secondary iframe effectively keeps a cache of all of the callbacks. This is done because we don’t want to pass an actual function across the wire. When the modal is closed, the Trello web client reaches back out to the iframe and says, “call that function I told you to hold onto and then let it go.”

However, when you open a modal from a secondary iframe, the modal opens and we remove the secondary iframe from the DOM. The web client still sends the message to call the callback and then release it, but because the secondary iframe has been destroyed, the message goes unreceived.

The reason this doesn’t happen when you open a modal directly from a capability (for instance, as the callback for a board button) is because the connectorUrl is a hidden iframe and never destroyed (unless the Power-Up is disabled). Theoretically, we could try to be really clever and hold onto iframes that have callbacks, but this isn’t something we’ve explored at all.

Relatedly, we do manage a popup stack for you if you open a popup from a popup. So the unexpected behavior only occurs when you bring a modal or board bar into the mix.

3

Thank you for the expanded answer.

On your last point about the pop up stack I’m a bit confused.
In my experiments the callback on t.popup() is never called even if I open it using the “t” context given to a capability handler. Also, the “callback” option is not in the documentation for the t.popup().

So my question is: Should the “callback” option work for the t.popup() ?

4

No, I was wrong. Edited my answer. Disregard that last bit! :sweat_smile: