Every time I try to launch the application, it is saying it is from an unidentified developer, and then throws up a Javascript error that does not go away. I have uninstalled and re-installed it multiple times.
Pictures tell the whole story
When I open it (either by Double Clicking, Right-Click->Open, or Open from App Store):

Then it does this weird error that cannot be removed (probably because it does not have access rights):

Launch the application
On macOS Catalina, all apps have to be notarized by Apple
Source
Is there a workaround?
On macOS Catalina, all apps have to be notarized by Apple
Source
Are you already working on getting it notarized? Catalina launch will be very soon.
I am confused. You have the app in the Mac App Store already. I don't see how this would be at all difficult to handle.
i found a workaround, for now download the app directly from the website instead installing from the app store
@lazyants, worked like a charm!
i think this is still not resolved, isn't it? I had to download the app once more from the website, because the one from the app store doesn't work anymore.
Confirmed, a fresh download from the app store still fails with this error.
Downloading directly from the site, works on current version of MacOS Catalina 10.15 (19A583)
My temporary solution:
sudo xattr -cr /Applications/Rocket.Chat.app
sudo codesign --force --deep --sign - /Applications/Rocket.Chat.app
https://developer.apple.com/news/?id=06032019i Here's the press release concerning this issue.
Most helpful comment
i found a workaround, for now download the app directly from the website instead installing from the app store