To add some further context that isn't written here, the exploit developer here has been tinkering around with v8 for a while. Last year he published a vulnerable VM to HackTheBox (a CTF platform) called RopeTwo[1], where the initial entry point looked extremely similar to this. Its largely regarded as one of the most difficult challenges to solve to date.
1. https://www.hackthebox.eu/home/machines/profile/260