javascript callback function synchronise

Question

I am currently working on an Alexa Skill to collect data from an SAP system. Because of a callback in my function to collect the data, Alexa speaks, before the speakOutput variable gets updated.

const LagerhueteIntent = {
 canHandle(handlerInput) {
 return Alexa.getRequestType(handlerInput.requestEnvelope) === 'IntentRequest' &&
 Alexa.getIntentName(handlerInput.requestEnvelope) === 'LagerhueteIntent';
 },
 handle(handlerInput) {
 let speakOutput;
 console.log("test");
 findWarehouseKeepers(function(warehouseKeeper) {
 console.log(warehouseKeeper);
 speakOutput = "Die Lagerhüter sind die Produkte mit den Ids" + warehouseKeeper;
 console.log(speakOutput);
 });
 return handlerInput.responseBuilder
 .speak(speakOutput)
 //.reprompt('add a reprompt if you want to keep the session open for the user to respond')
 .getResponse();
 }
};

With my function:

function findWarehouseKeepers(callback) {
 var args = getArgs();
 console.log(args);
 var Client = require('node-rest-client').Client;
 var client = new Client();
 client.get("http://XXXXXXXX$format=json", args, function(data, response) {
 let validValuesList = new List([]);
 data.d.results.forEach(function(data) {
 validValuesList.add(data.ProductId);
 });
 console.log(validValuesList);
 let validValuesAsArray = validValuesList.toArray();
 console.log(validValuesAsArray);
 callback(validValuesAsArray);
 });
}

How can I get my function synchronized, so the speakOutput variable gets updated before the next code gets executed? Thanks in advance.

• James: Forget trying to return something from a function that only initializes an async operation. IMO do the .speak part inside the callback function that you provide to findWarehouseKeepers.
• Bergi: Can handle return a promise for the response?
• Felix Kling: @Bergi: Yes. I was just researching this. developer.amazon.com/en-US/docs/alexa/…

Answer 1

As per documentation, handle can return a promise, which will allow you to build the response once you received the data.

Ideally you would change findWarehouseKeepers to return a promise, but here is an example with minimal changes to your code:

handle(handlerInput) {
 return new Promise(resolve => {
 findWarehouseKeepers(warehouseKeeper => {
 const speakOutput = "Die Lagerhüter sind die Produkte mit den Ids" + warehouseKeeper;
 resolve(
 handlerInput.responseBuilder
 .speak(speakOutput)
 .getResponse()
 );
 });
 });
}

Of course you would also want to think about what to do if the request fails, i.e. you want to reject the promise.

---

If you change findWarehouseKeepers to return a promise then you could probably write declare handle as async (I don't know in which environment this code runs) and write the code in a way that looks synchronous:

async handle(handlerInput) {
 const warehouseKeeper = await findWarehouseKeepers();
 return handlerInput.responseBuilder
 .speak("Die Lagerhüter sind die Produkte mit den Ids" + warehouseKeeper)
 .getResponse()
}