index.js

var APP_ID = undefined;
var ROSLIB = require('roslib');
var Alexa = require('alexa-sdk');
var EMMITER = require('eventemitter2');
var HELP_REPROMPT = "What can I help you with?";
var HELP_MESSAGE = "You can say forward, backward turn left or turn right... What can I help you with?";
var FORWARD = "forward";
var BACKWARD = "backward";
var TURN_LEFT = "turn left";
var TURN_RIGHT = "turn right";
var STOP_MESSAGE = "Goodbye!";
var RECIPE_NOT_FOUND_MESSAGE = "I\'m sorry, I currently do not know that command. Please try again.";
var RECIPE_NOT_FOUND_REPROMPT = "What else can I help with?";


//ROS functionallity
var ros = new ROSLIB.Ros({
    url: 'ws://localhost:9090'
});

ros.on('connection', function () {
    console.log('Connected to websocket server.');
});

ros.on('error', function (error) {
    console.log('Error connecting to websocket server: ', error);
});

ros.on('close', function () {
    console.log('Connection to websocket server closed.');
});

var cmdVel = new ROSLIB.Topic({
    ros: ros,
    name: '/turtle1/cmd_vel',
    messageType: 'geometry_msgs/Twist'
});

var twistf = new ROSLIB.Message({
    linear: {
        x: 2.0,
        y: 0.0,
        z: 0.0
    },
    angular: {
        x: 0.0,
        y: 0.0,
        z: 0.0
    }
});
var twistb = new ROSLIB.Message({
    linear: {
        x: -2.0,
        y: 0.0,
        z: 0.0
    },
    angular: {
        x: 0.0,
        y: 0.0,
        z: 0.0
    }
});

var twistl = new ROSLIB.Message({
    linear: {
        x: 0.0,
        y: 0.0,
        z: 0.0
    },
    angular: {
        x: 0.0,
        y: 0.0,
        z: 1.6
    }
});
var twistr = new ROSLIB.Message({
    linear: {
        x: 0.0,
        y: 0.0,
        z: 0.0
    },
    angular: {
        x: 0.0,
        y: 0.0,
        z: -1.5
    }
});

//Amazon Alexa handlers
var handlers = {
    'LaunchRequest': function () {
        console.log('In Launch Request');
        talkmsg = 'Where do you want to go?';
        this.emit(':tell', talkmsg);
    },

    'MessageIntent': function () {
        var cmd = this.event.request.intent.slots.Item.value;
       
        if (cmd === FORWARD) {
            cmdVel.publish(twistf);
            this.emit(':ask', 'Moving forward...Please say another command or cancel if you want to exit');
        }
        else if (cmd === BACKWARD) {
            cmdVel.publish(twistb);
            this.emit(':ask', 'Moving backward...Please say another command or cancel if you want to exit');
        }
        else if (cmd === TURN_LEFT) {
            cmdVel.publish(twistl);
            this.emit(':ask', 'Turning left...Please say another command or cancel if you want to exit');
        }
        else if (cmd === TURN_RIGHT) {
            cmdVel.publish(twistr);
            this.emit(':ask', 'Turning right...Please say another command or cancel if you want to exit');
        }
        else {
            let speechOutput = RECIPE_NOT_FOUND_MESSAGE;
            const repromptSpeech = RECIPE_NOT_FOUND_REPROMPT;
            this.emit(':ask', speechOutput, repromptSpeech);
        }

    },
    'AMAZON.HelpIntent': function () {
        var speechOutput = HELP_MESSAGE;
        var reprompt = HELP_REPROMPT;
        this.emit(':ask', speechOutput, reprompt);
    },
    'AMAZON.CancelIntent': function () {
        this.emit(':tell', STOP_MESSAGE);
    },
    'AMAZON.StopIntent': function () {
        this.emit(':tell', STOP_MESSAGE);
    }
};
exports.handler = function (event, context, callback) {
    var alexa = Alexa.handler(event, context);
    alexa.APP_ID = APP_ID;
    alexa.registerHandlers(handlers);
    alexa.execute();
};