mqtt-test.js

var mqtt = require("mqtt");
var client = mqtt.connect("mqtt://127.0.0.1");
client.on("connect", function() {
  client.subscribe("presence");
  client.publish("presence", "Hello mqtt");
});
client.on("message", function(topic, message) {
  // message is Buffer
  console.log(message.toString());
  client.end();
});

mqtt-server.js

var mosca = require("mosca");
var settings = {
  port: 1883,
  backend: {}
};
var server = new mosca.Server(settings);
server.on("clientConnected", function(client) {
  console.log("client connected", client.id);
});
server.on("published", function(packet, client) {
  console.log("Published", packet.payload);
});
server.on("ready", setup);
function setup() {
  console.log("Mosca server is up and running");
}

package.json

{
  "name": "mqtt-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "mosca": "^2.8.3",
    "mqtt": "^3.0.0"
  }
}