Stuck after track command about adbkit HOT 2 OPEN

var adb = require("adbkit");
var util = require("util");
var Promise = require("bluebird");

try {
    var Electron = require("electron");
} catch (e) {}

var main = function () {
    //console.log("Creating ADB client");

    adbClient = adb.createClient();

    adbClient.trackDevices()
        .then((tracker) => {
            tracker.on("add", (device) => {
                //console.log("Added: " + device.id);

                Promise.join(
                    adbClient.getFeatures(device.id),
                    adbClient.getProperties(device.id),
                    (features, props) => {
                        console.log("Features: " + util.inspect(features));
                        console.log("Properties: " + util.inspect(props));
                    });
            });
            tracker.on("remove", (device) => {
                console.log("Removed: " + device.id);
            });
            tracker.on("change", (device) => {
                console.log("Changed: " + device.id);
            });
            tracker.on("error", (err) => {
                console.log("Error: " + err);
            });
        });
};

if (Electron)
    Electron.app.on("ready", main);
else
    main();