Alexa-SDK Audio Issue - node.js

Question

I've been trying to make an alexa skill that involves audio. I found a great guide here.
Here is their example code:
var stateByUser = {};
var podcastURL = "https://feeds.soundcloud.com/stream/309340878-user-652822799-episode-010-building-an-alexa-skill-with-flask-ask-with-john-wheeler.mp3";
// Entry-point for the Lambda
exports.handler = function(event, context) {
var player = new SimplePlayer(event, context);
player.handle();
};
// The SimplePlayer has helpful routines for interacting with Alexa, within minimal overhead
var SimplePlayer = function (event, context) {
this.event = event;
this.context = context;
};
// Handles an incoming Alexa request
SimplePlayer.prototype.handle = function () {
var requestType = this.event.request.type;
var userId = this.event.context ? this.event.context.System.user.userId : this.event.session.user.userId;
var response = null;
// On launch, we tell the user what they can do (Play audio :-))
if (requestType === "LaunchRequest") {
this.say("Welcome to the Simple Audio Player. Say Play to play some audio!", "You can say Play");
// Handle Intents here - Play, Pause and Resume is all for now
} else if (requestType === "IntentRequest") {
var intent = this.event.request.intent;
if (intent.name === "Play") {
this.play(podcastURL, 0);
} else if (intent.name === "AMAZON.PauseIntent") {
// When we receive a Pause Intent, we need to issue a stop directive
// Otherwise, it will resume playing - essentially, we are confirming the user's action
this.stop();
} else if (intent.name === "AMAZON.ResumeIntent") {
var lastPlayed = this.load(userId);
var offsetInMilliseconds = 0;
if (lastPlayed !== null) {
offsetInMilliseconds = lastPlayed.request.offsetInMilliseconds;
}
this.play(podcastURL, offsetInMilliseconds);
}
} else if (requestType === "AudioPlayer.PlaybackStopped") {
// We save off the PlaybackStopped Intent, so we know what was last playing
this.save(userId, this.event);
}
};
/**
* Creates a proper Alexa response using Text-To-Speech
* #param message
* #param repromptMessage
*/
SimplePlayer.prototype.say = function (message, repromptMessage) {
var response = {
version: "1.0",
response: {
shouldEndSession: false,
outputSpeech: {
type: "SSML",
ssml: "<speak> " + message + " </speak>"
},
reprompt: {
outputSpeech: {
type: "SSML",
ssml: "<speak> " + message + " </speak>"
}
}
}
}
this.context.succeed(response);
};
/**
* Plays a particular track, from specific offset
* #param audioURL The URL to play
* #param offsetInMilliseconds The point from which to play - we set this to something other than zero when resuming
*/
SimplePlayer.prototype.play = function (audioURL, offsetInMilliseconds) {
var response = {
version: "1.0",
response: {
shouldEndSession: true,
directives: [
{
type: "AudioPlayer.Play",
playBehavior: "REPLACE_ALL", // Setting to REPLACE_ALL means that this track will start playing immediately
audioItem: {
stream: {
url: audioURL,
token: "0", // Unique token for the track - needed when queueing multiple tracks
expectedPreviousToken: null, // The expected previous token - when using queues, ensures safety
offsetInMilliseconds: offsetInMilliseconds
}
}
}
]
}
}
this.context.succeed(response);
};
// Stops the playback of Audio
SimplePlayer.prototype.stop = function () {
var response = {
version: "1.0",
response: {
shouldEndSession: true,
directives: [
{
type: "AudioPlayer.Stop"
}
]
}
}
this.context.succeed(response);
};
// Saves information into our super simple, not-production-grade cache
SimplePlayer.prototype.save = function (userId, state) {
console.log("Save: " + userId);
stateByUser[userId] = state;
};
// Load information from our super simple, not-production-grade cache
SimplePlayer.prototype.load = function (userId) {
console.log("Load: " + userId);
var state = null;
if (userId in stateByUser) {
state = stateByUser[userId];
console.log("Loaded " + userId + " State: " + state);
}
return state;
};
I am trying to refactor this code so that it follows a similar format to the trivia skills example that amazon provides. However, when I run my refactored code I get an error saying
TypeError: Cannot set property 'say' of undefined
at Object.<anonymous> (/Users/Rob/Desktop/super-simple-audio-player/index.js:47:28)
Here is my attempt at refactoring
"use strict";
var stateByUser = {};
var podcastURL = "https://p.scdn.co/mp3-preview/2385471a5d35709ad90e368dacabe4082af4541a?cid=null";
var Alexa = require("alexa-sdk");
// Entry-point for the Lambda
exports.handler = function(event, context) {
var alexa = Alexa.handler(event, context);
alexa.registerHandlers(SimplePlayer);
alexa.execute();
};
// The SimplePlayer has helpful routines for interacting with Alexa, within minimal overhead
var SimplePlayer = {
"LaunchRequest": function () {
this.emit(":tell","Welcome to the Simple Audio Player. Say play to begin.");
},
"Play": function() {
this.play(podcastURL, 0);
},
"AMAZON.PauseIntent": function() {
this.stop();
},
"AMAZON.ResumeIntent": function () {
var lastPlayed = this.load(userId);
var offsetInMilliseconds = 0;
if (lastPlayed !== null) {
offsetInMilliseconds = lastPlayed.request.offsetInMilliseconds;
}
this.play(podcastURL, offsetInMilliseconds);
},
"AudioPlayer.PlaybackStopped": function () {
this.save(userId, this.event);
}
};
// Handles an incoming Alexa request
SimplePlayer.prototype.say = function (message, repromptMessage) {
var response = {
version: "1.0",
response: {
shouldEndSession: false,
outputSpeech: {
type: "SSML",
ssml: "<speak> " + message + " </speak>"
},
reprompt: {
outputSpeech: {
type: "SSML",
ssml: "<speak> " + message + " </speak>"
}
}
}
}
this.context.succeed(response);
};
/**
* Plays a particular track, from specific offset
* #param audioURL The URL to play
* #param offsetInMilliseconds The point from which to play - we set this to something other than zero when resuming
*/
SimplePlayer.prototype.play = function (audioURL, offsetInMilliseconds) {
var response = {
version: "1.0",
response: {
shouldEndSession: true,
directives: [
{
type: "AudioPlayer.Play",
playBehavior: "REPLACE_ALL", // Setting to REPLACE_ALL means that this track will start playing immediately
audioItem: {
stream: {
url: audioURL,
token: "0", // Unique token for the track - needed when queueing multiple tracks
expectedPreviousToken: null, // The expected previous token - when using queues, ensures safety
offsetInMilliseconds: offsetInMilliseconds
}
}
}
]
}
}
this.context.succeed(response);
};
// Stops the playback of Audio
SimplePlayer.prototype.stop = function () {
var response = {
version: "1.0",
response: {
shouldEndSession: true,
directives: [
{
type: "AudioPlayer.Stop"
}
]
}
}
this.context.succeed(response);
};
// Saves information into our super simple, not-production-grade cache
SimplePlayer.prototype.save = function (userId, state) {
console.log("Save: " + userId);
stateByUser[userId] = state;
};
// Load information from our super simple, not-production-grade cache
SimplePlayer.prototype.load = function (userId) {
console.log("Load: " + userId);
var state = null;
if (userId in stateByUser) {
state = stateByUser[userId];
console.log("Loaded " + userId + " State: " + state);
}
return state;
};
I've added alexa-sdk and changed the exports.handler and the simplePlayer.prototype.handler(). Any thoughts as to why it is not working?
Thanks in advance

Answer 1

I actually created the project you reference. Glad you are finding it useful.
In re-factoring the project, you changed it from prototype-style JS object to an object literal. Both are viable approaches, but the object literal becomes a problem when holding the state for a particular request (the event and context fields in particular).
It also means that the prototype methods defined in the project are not available from the object literal definition. You need to instantiate SimplePlayer (by calling new SimplePlayer(event, context)) before you will get those.
If you want to understand the trade-off between these approaches better, you can read here:
Object literal vs constructor+prototype
Here is an example of working with the Alexa SDK consistent with my project. It defines the "LaunchRequest" function as a prototype function rather than simply a property:
SimplePlayer.prototype.LaunchRequest = function () {
this.emit(":tell", "Welcome to the Simple Audio Player. Say play to begin.");
};
You also need to make sure to instantiate the SimplePlayer (not just reference it). When registering it, it should look like this:
alexa.registerHandlers(new SimplePlayer(event, context));
Hope that makes sense, and good luck with it! Let me know how it goes (I can always be reached at https://gitter.im/bespoken/bst)