How to fix node.js on macOS write to file permission denied error?

I set up node.js to write to file on its local folder as such:

Note: I have already use sudo chmod 755 req.txt and sudo chmod 755 bodyhead.txt to set the permission of the file to be writable.

fs.writeFile('/req.txt', req + '\r\n!ended!\r\n', function(err) {
  if(err) {
    return console.log(err);
  }
});
fs.writeFile('/bodyhead.txt', bodyhead + '\r\n!ended!\r\n', function(err) {
  if(err) {
    return console.log(err);
  }
});

And received:

{ Error: EACCES: permission denied, open '/req.txt' errno: -13, code: 'EACCES', syscall: 'open', path: '/req.txt' }

as well as

{ Error: EACCES: permission denied, open '/bodyhead.txt' errno: -13, code: 'EACCES', syscall: 'open', path: '/bodyhead.txt' }