.js

'use strict';

var Promise = require('bluebird');

modeminit({
  ports: 
   [ { DEVNAME: '/dev/ttyUSB1',
       ID_MODEL: 'E173s 3G broadband stick (modem on)' },
     { DEVNAME: '/dev/ttyUSB0',
       ID_MODEL: 'E173s 3G broadband stick (modem on)' },
     { DEVNAME: '/dev/ttyUSB2',
       ID_MODEL: 'E173s 3G broadband stick (modem on)' } ]
}).then(function (port) {
    console.log("initialized with port:", port);
});

function modem(cfg) {
    this.count = 0;
    this.ports = cfg.ports;
}
modem.prototype.openSerial = function (port) {
    if (!this.count++) {
        return Promise.resolve(null);
    }
    return Promise.resolve('Success on port '+port.DEVNAME);
};

function modeminit(mo) {
    var m = new modem(mo);
    return Promise.reduce(mo.ports, function (retval, port) {
        return retval || m.openSerial(port); 
    }, null)
    .then(function (port) { 
        if (!port) { 
            throw new Error('couldn\'t open anything'); 
        }
        return port;
    });
}