/usr/lib/x86_64-linux-gnu/libjavascriptcoregtk-4.0.so.18 is in libjavascriptcoregtk-4.0-18 2.18.6-1~deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libjavascriptcoregtk-4.0.so.18.6.15