The leading zero in 0777
indicates that the number is an octal number.
The number 777
in octal notation is the number 511
in decimal notation. fs.chmod(path, 0777)
and fs.chmod(path, 511)
do the same thing, but fs.chmod(path, 777)
does not.
The reason for your confusion is that you assumed the file access mode 777
is a decimal number. You might want to read more about the unix chmod program and file system permissions.