Create a file if it doesn't already exist

I think the answer is:

Just open the file and handle the error when it's not there.

Try something like:

function createFile(filename) {
  fs.open(filename,'r',function(err, fd){
    if (err) {
      fs.writeFile(filename, '', function(err) {
          if(err) {
              console.log(err);
          }
          console.log("The file was saved!");
      });
    } else {
      console.log("The file exists!");
    }
  });
}

fs.closeSync(fs.openSync('/var/log/my.log', 'a'))