simple coap handling when server is down(timeout)

coap.js

var sensorLib = require("node-dht-sensor");
var temp = {
    read: function() {
            var a = sensorLib.read(11,4);
            return a.temperature.toFixed(1);
    }
};
var hum = {
    read: function() {
            var b = sensorLib.read(11,4);
            return b.humidity.toFixed(1);
    }
};

var coapp = function () {
    const coap = require('coap')
    const cron = require('node-cron');
    var payload = {
        protocol: "coap",
        timestamp: new Date().toISOString(),
        topic: "dht/pi2A",
        sensor: {
            tipe: "esp8266",
            index: "cocoap",
            ip: "192.168.42.42",
            module: "dht11"
        },
        humidity: {
            value: hum.read(),
            unit: "%"
        },
        temperature: {
            value: temp.read(),
            unit: "celcius"
        }
    }

    var req = coap.request({host: '192.168.42.101', port: '5683', pathname: '/r/dht/pi2A', method: 'post', retrySend: 0})
    req.write(JSON.stringify(payload))
    req.on("response", (res) => {console.log(res)})

    // err has two attribtues, name and message, this CoaP library based on HTTP connection
    // using following answer to catch the error 
    // error catch : https://stackoverflow.com/questions/4328540/how-to-catch-http-client-request-exceptions-in-node-js
    // error prototype : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/prototype
    req.on("error", (err) => {
        console.log(err.message);
        console.log("Sending data to backup server")
        var reqOnBackupServer = coap.
        request({
            host: '192.168.42.100',
            port: '5683',
            pathname: '/r/backup/dht/pi2A/',
            method: 'post'
        })
        reqOnBackupServer.on("response", (res) => {
            console.log("Success sending to backup server")
            process.exit(0)
        })
        reqOnBackupServer.write(JSON.stringify(payload))
        reqOnBackupServer.end()
    })
    req.end()

}
module.exports = coapp;