Cannot get output of child_process.spawn with interactive scripts - node.js

Question

I cannot get any output in the following code:
var spawn = require('child_process').spawn,
script = 'ftp',
child = spawn(script);
child.stdout.on('data', function (data) {
console.log('stdout: ' + data);
});
child.stderr.on('data', function (data) {
console.log('stderr: ' + data);
});
child.on('close', function (code) {
console.log('child process exited with code ' + code);
});
It works for normal scripts such as 'ls', 'pwd' etc. But not for interactive programs such as 'ftp', 'telnet'. Any suggestions?
Edit:
Take another script for example:
#!/usr/bin/env python
name = raw_input("your name>")
print name
When spawn this script, I wish to fetch the prompt "your name>" with the data event, so that I can latter input something into stdin.
The problem is that I got nothing in the data event, and it seemed that none of these events are triggered.

Answer 1

ls, cat is controllable via input output and error stream.
ftp, telnet is controllable indirectly via tty.
The protocol is also base on input/output stream but it is more complicated. You can use available package to handle that protocol.
https://github.com/chjj/pty.js
var pty = require('pty.js');
var term = pty.spawn('ftp', [], options);
term.on('data', function(data) {
console.log(data);
});
term.write(ftpCmd + '\r');
The author of pty have some interesting examples, he forward pty to web via web socket, including terminal games:
https://github.com/chjj/tty.js

Answer 2

In interactive mode there is a command interpreter that reads user input from stdin, then accodingly prints output. So you have to write to stdin to do something. For example add following lines to your code with telnet command:
child.stdin.write('?\n');
child.stdin.write('quit\n');
Output:
stdout: Commands may be abbreviated. Commands are:
! cr mdir proxy send
$ delete mget sendport site
account debug mkdir put size
append dir mls pwd status
ascii disconnect mode quit struct
bell form modtime quote system
binary get mput recv sunique
bye glob newer reget tenex
case hash nmap rstatus trace
ccc help nlist rhelp type
cd idle ntrans rename user
cdup image open reset umask
chmod lcd passive restart verbose
clear ls private rmdir ?
close macdef prompt runique
cprotect mdelete protect safe
child process exited with code 0