Node: Read spawn stderr/stdout after quick exit event?

Question

I'm using Node's spawn to create a new process. Sometimes this process will exit very quickly with an error code and a message on stderr. It appears that stderr is getting lost in this quick turnaround. I've tried this:

    reader.stderr.on('data', function (buf) {
        console.log('stderr message: ' + buf);
    });

    reader.on('exit', function (code, signal) {
        console.log('Exit');
    });

Output:

   Exit
   stderr message: ERROR: Missing required option for command.

I also tried reading it in the exit listener, but no luck:

     reader.on('exit', function (code, signal) {
        console.log('Exit');
        console.log('stderr: ' + reader.stderr.read());
    });

Output:

    Exit
    stderr: null

So, it appears the problem is that the stderr output is too slow, and is late after the exit event where I need that information. How can I fix this?

Answer 1

Taken from the child_process docs for exit:

Note that the child process stdio streams might still be open.

They then describe the close event:

This event is emitted when the stdio streams of a child process have all terminated. This is distinct from 'exit', since multiple processes might share the same stdio streams.

So it looks like you should be using close, not exit.