Repeat sentence in Dialogflow for VUI without external libraries (multivocal/VoiceRepeater) - node.js

Question

I am trying to make my VUI repeat its last sentence when prompted for this (e.g. when user says 'I'm sorry, I did not hear you). I have tried to do this using the libraries multivocal and VoiceRepeater but this is not working for me so I want to implement it according to this guide: https://developers.google.com/assistant/conversational/tips
I have already taken the following steps:
Created an intent called 'Repeat'.
Added training phrases for the intent
Enabled webhook call for this intent
In Node.js added the following code:
// See https://github.com/dialogflow/dialogflow-fulfillment-nodejs
// for Dialogflow fulfillment library docs, samples, and to report issues
'use strict';
const functions = require('firebase-functions');
const {WebhookClient} = require('dialogflow-fulfillment');
const {Card, Suggestion} = require('dialogflow-fulfillment');
process.env.DEBUG = 'dialogflow:debug'; // enables lib debugging statements
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
const agent = new WebhookClient({ request, response });
function repeat(agent) {
const REPEAT_PREFIX = [
'Sorry, Ik zei ',
'Laat me het herhalen: ',
'Wat ik zei is'
];
const reply = (agent, inputPrompt, noInputPrompts) => {
agent.data.lastPrompt = inputPrompt;
agent.data.lastNoInputPrompts = noInputPrompts;
agent.ask(inputPrompt, noInputPrompts);
};
// Intent handlers
const normalIntent = (agent) => {
reply(agent, 'Hey this is a question', 'Ik zie niks');
};
let repeatPrefix = promptFetch.getRepeatPrefix(); // randomly chooses from REPEAT_PREFIX
// Move SSML start tags over
if (agent.data.lastPrompt.startsWith(promptFetch.getSSMLPrefix())) {
agent.data.lastPrompt =
agent.data.lastPrompt.slice(promptFetch.getSSMLPrefix().length);
repeatPrefix = promptFetch.getSSMLPrefix() + repeatPrefix;
}
agent.add(repeatPrefix + agent.data.lastPrompt,
agent.data.lastNoInputPrompts);
}
// Run the proper function handler based on the matched Dialogflow intent name
let intentMap = new Map();
intentMap.set('Repeat', repeat);
agent.handleRequest(intentMap);
});
Unfortunately, this does not work for me, one error I get it that it says 'FetchPrompt is not defined', which I don't understand. I know the setup is okay because this code does return: 'this is a response from the webhook' if I prompt the VUI for repeating its sentence:
// See https://github.com/dialogflow/dialogflow-fulfillment-nodejs
// for Dialogflow fulfillment library docs, samples, and to report issues
'use strict';
const functions = require('firebase-functions');
const {WebhookClient} = require('dialogflow-fulfillment');
const {Card, Suggestion} = require('dialogflow-fulfillment');
process.env.DEBUG = 'dialogflow:debug'; // enables lib debugging statements
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
const agent = new WebhookClient({ request, response });
function repeat(agent) {
agent.add('this is a response from the webhook');
}
// Run the proper function handler based on the matched Dialogflow intent name
let intentMap = new Map();
intentMap.set('Repeat', repeat);
agent.handleRequest(intentMap);
});

Answer 1

As #Prisoner points out, your code is intended to work only with dialogflow-fulfillment but you based it on an actions-on-google example. That's the cause of the code errors.
Some things you want to do are only available for Actions on Google, for example, the object conv contains functionality that only works when executed within Google Assistant, and this is the core of the problem.
Even if you fix the code, the example you're following uses conv.data as a temporary storage for the last reply of the agent during the conversation; however conv.data functionality is not availabe outside Google Assistant platforms, and, at the moment, Dialogflow doesn't have a straightforward approach to get the agent last response.
If you don't want to integrate with Google Assistant, then you'd need to find a suitable workaround to store your agent last reply. Here's a question where this issue with the temporary storage was discussed, maybe you can use it as a reference.
For your use case, I think you could get away with it by using contexts to store the last replies.