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This script will automatically attempt to rejoin a full room.
< Opiniones de Automatic Re-Join · Bonk.io
But wait, you have to give credit to UnmatchedBracket; the script is a derived work from https://greasyfork.org/en/scripts/449381-auto-rejoin/code, isn't it? You just changed the intervals and then shortened down line 18 with a regex?
Update: Credit has now been added
Nice!
The auto joining works and is about as fast as if you were trying to rejoin over and over manually, giving you the benefit of leaving the tab open while you're doing something else. Pressing the cancel button on the loading window successfully stops the script from attempting further rejoins.
(I didn't test it on locked rooms but I assume that that works too. Judging from the code, I think you type in the password once and then it reuses it each time)