How do I stream response in express?

You don’t need a readable stream instance, just use res.write():

res.write("USERID,NAME,FBID,ACCOUNT,SUBSCRIPTION,PRICE,STATE,TIMEPERIOD\n");

for (var i = 0; i < 10; i++) {
    res.write("23,John Doe,1234,500,SUBSCRIPITON,100,ACTIVE,30\n");
}

res.end();

This works because in Express, res is based on Node’s own http.serverResponse, so it inherits all its methods (like write).