Node-SerialPort Issue w/ Multiple Writes - node.js

Question

When I pass an array with 1 element everything works great, when I pass one with two (max for our use case) I get the following error:
There's no write queue for that file descriptor (after write)!
Here is my code:
exports.triggerPhysical = function(state, alerts) {
console.dir("IN PHYSICAL");
console.dir(alerts);
SerialPort.list(function(err, ports) {
var port = {};
for(var i = 0; i < ports.length; i++) {
try {
if(typeof ports[i].manufacturer != 'undefined' && ports[i].manufacturer.includes("Numato")) {
port = ports[i];
}
} catch(err) {
console.dir(err);
}
}
var numato = new SerialPort(port.comName, {baudrate : 19200}, function(err) {
if(err) {
return console.dir(err);
}
console.dir('calling write');
for(var j = 0; j < alerts.length; j++) {
numato.write('relay ' + state + ' ' + alerts[j].index + '\r', function(err) {
if(err) {
console.dir('error writing');
console.dir(err);
}
console.dir('serial message written');
});
}
numato.close();
return true;
});
});
}
First write works great, second one fails. I am guessing there is an obvious solution but I am not finding it. Any insight would be much appreciated.

Answer 1

I ended up doing two things to resolve this issue. First I upgraded to version 5.x of the node-serialport library.
Second, I changed my code to the following:
exports.triggerPhysical = function(state, alerts) {
var port = new SerialPort('/dev/ttyACM0');
port.on("open", function() {
alerts.forEach(function(alert, idx) {
str = 'relay ' + state + ' ' + alert.index + '\r';
port.write(str, function(err, results) {
if(err) {
console.dir("err writing");
console.dir(err);
} else {
console.dir(results);
}
});
});
})
port.drain(writeDone);
function writeDone() {
console.dir("In writeDone");
port.close();
}
}
I am now able to do consecutive writes without causing any errors and the port doesn't end up in a weird locked state.