nodejs process.setgid, process.setuid behavior with fs module - node.js

Question

directory:
drwxrwxr-x 2 alex alex 4096 Aug 3 12:03 ./
drwxr-xr-x 17 alex alex 4096 Aug 3 11:18 ../
-rwx------ 1 root root 19 Aug 3 11:24 privilegedStuff*
-rwxrwx--- 1 root root 28 Aug 3 12:10 privilegedStuff1*
-rwxrwxr-x 1 alex alex 830 Aug 3 12:12 test.js*
test.js:
#!/usr/bin/env node
var fs = require('fs');
console.log(' user id: ', process.getuid());
console.log(' group id: ', process.getgid());
console.log(' user effective id: ', process.getegid());
console.log('group effective id: ', process.getegid());
console.log('\n switching user and group...\n');
process.setgid(1000);
process.setegid(1000);
process.setuid(1000);
process.seteuid(1000);
console.log(' user id: ', process.getuid());
console.log(' group id: ', process.getgid());
console.log(' user effective id: ', process.getegid());
console.log('group effective id: ', process.getegid());
console.log('\n output: \n');
console.log(fs.readFileSync('./privilegedStuff1', 'utf8'))
// this throws error as expected so I commented that
// console.log(fs.readFileSync('./privilegedStuff', 'utf8'))
privilegedStuff1:
content of privilegedStuff1
result:
alex#hp:/apps/test$ sudo ./test.js
user id: 0
group id: 0
user effective id: 0
group effective id: 0
switching user and group...
user id: 1000
group id: 1000
user effective id: 1000
group effective id: 1000
output:
content of privilegedStuff1
so what I don't understand is why node doesn't throw an error as it does nicely with privilegedStuff file? What am I missing?
alex#hp:/apps/test$ groups
alex adm cdrom sudo dip plugdev lpadmin sambashare
alex#hp:/apps/test$ cat privilegedStuff1
cat: privilegedStuff1: Permission denied
alex#hp:/apps/test$ sudo -s
root#hp:/apps/test# groups
root

Answer 1

In my test, I don't have such problem.
Can you enter the following command and show the result:
ls -l privilegedStuff1
id