I use process.stdout.write in the output of the program so that the output is in one line.

See this example:

while(true) {
  process.stdout.write("X");
  process.stdout.write("Y");
  console.log("");
  await new Promise(resolve => setTimeout(resolve, 1000));
}

I try to see the output with pm2 log. I expect XY to fall together in a line. But in practice, sometimes Y appears in the next line:

# pm2 log app
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | X
60|app  | Y
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | X
60|app  | Y
60|app  | X
60|app  | Y
60|app  | XY
60|app  | XY
60|app  | XY
60|app  | XY

But they are saved correctly in the log file:

# tailf -f /root/.pm2/logs/app-out.log
XY
XY
XY
XY
XY
XY
XY

In the next example, I add a very short pause of 1ms:

while(true) {
  process.stdout.write("X");
  await new Promise(resolve => setTimeout(resolve, 1)); //added this line
  process.stdout.write("Y");
  console.log("");
  await new Promise(resolve => setTimeout(resolve, 1000));
}

You can see that the output is permanently spaced between X and Y, which makes the problem worse:

# pm2 log app
60|app  | X
60|app  | Y
60|app  | X
60|app  | Y
60|app  | X
60|app  | Y
60|app  | X
60|app  | Y

How can I always be sure in the pm2 log command that the output logs are used wherever process.stdout.write is used and that it doesn’t appear until n or console.log is reached on the next line. Just like what is saved in the file and I can see it with the tail -f command?