We have a collection field that contains a bunch of single line fields. These single line fields have "fill Field X with values from column Y" lookup rules.

Whenever the user clicks the Add button to add another item to the collection, the entire UI freezes. The new fields show up only after the lookup is done. This is an issue because the lookups can take ~5 seconds to complete, during which the user gets confused because their browser hangs.

We tried adding a loading overlay gif when the user clicks the Add button so that they can at least know stuff is happening. The problem is that the gif does not show up until AFTER the lookup is done.

I did some debugging and found that this is because Forms performs the XHR synchronously, and synchronous requests cause most browser UIs to lock up. Even the scrollbars will stop functioning!

http://stackoverflow.com/questions/6015273/loading-gif-freezes-when-code-is-executing

We need an option in the lookup rules to have the lookup performed asynchronously (using the async: true option in Jquery's Ajax function).

Thank you for reading.