Stdout flush for NodeJS?

write returns true if the data has been flushed. If it returns false, you can wait for the 'drain' event.

I think there is no flush, because that would be a blocking operation.

In newer NodeJS versions, you can pass a callback to .write(), which will be called once the data is flushed:

sys.stdout.write('some data', () => {
  console.log('The data has been flushed');
});

This is exactly the same as checking .write() result and registering to the drain event:

let write = sys.stdout.write('some data');
if (!write) {
  sys.stdout.once('drain', () => {
    console.log('The data has been flushed');
  });
}

process.stdout is a WritableStream object, and the method WritableStream.write() automatically flushes the stream (unless it was explicitly corked). However, it will return true if the flush was successful, and false if the kernel buffer was full and it can't write yet. If you need to write several times in succession, you should handle the drain event.

See the documentation for write.