Callback returning empty array - Node.js

Question

I found these answers, but couldn't figure how to implement:

• Empty array in callback

• Node.js returning empty array

---

There is a 'callback' function in app.post at the bottom of the code. It is supposed to return the array created in httpsYtGetFunc. It returns the array with null value. Rest of the array is empty.

app.js

// Declaring variables for the function 'httpsYtGetFunc'
let apiKey = "";
let urlOfYtGetFunc = "";
let resultOfYtGetFunc = "";
let extractedResultOfYtGetFunc = [];

// This function GETs data, parses it, pushes required values in an array.
function httpsYtGetFunc(queryOfYtGetFunc, callback) {
  
  apiKey = "AI...MI"
  urlOfYtGetFunc = "https://www.googleapis.com/youtube/v3/search?key=" + apiKey + "&part=snippet&q=" + queryOfYtGetFunc + "&maxResults=4&order=relevance&type=video";

  // GETting data and storing it in chunks.
  https.get(urlOfYtGetFunc, (response) => {
    const chunks = []
    response.on('data', (d) => {
      chunks.push(d)
    })

    // Parsing the chunks
    response.on('end', () => {
      resultOfYtGetFunc = JSON.parse((Buffer.concat(chunks).toString()))
      // console.log(resultOfYtGetFunc)

      // Extracting useful data, and allocating it.
      for (i = 0; i < (resultOfYtGetFunc.items).length; i++) {
        extractedResultOfYtGetFunc.push(resultOfYtGetFunc.items[i].id.videoId);
        // console.log(extractedResultOfYtGetFunc);
      }
    })
  })
  callback (null, extractedResultOfYtGetFunc);
}

// Client makes POST request.
app.post("/", function(req, res) {

  query = "niall";

  // The callback
  ytQueryAppJs = httpsYtGetFunc(query, (ytQueryAppJs) => {
    console.log("ytQueryAppJs:");
    console.log(ytQueryAppJs);
  });
});

The console logs only null.

I believe that callback (null, extractedResultOfYtGetFunc); is running before https.get finishes.

Could somebody please suggest how to fix it and log all the results?

Thank you so much.

---

This is the link to original question:

How to synchronize 'time-consuming value allotment' of a variable, with the next commands, in nodejs?

Answer 1

response.on('end', () associate a function to the "end" event of https.get method. When you call callback (null, extractedResultOfYtGetFunc); outside of the https.get() block, the https request has not been finish yet, and the extractedResultOfYtGetFunc array is empty.

You need to move the callback function to the response.on('end') block

function httpsYtGetFunc(queryOfYtGetFunc, callback) {
  apiKey = "AI...MI"
  urlOfYtGetFunc = "https://www.googleapis.com/youtube/v3/search?key=" + apiKey + "&part=snippet&q=" + queryOfYtGetFunc + "&maxResults=4&order=relevance&type=video";

  // GETting data and storing it in chunks.
  https.get(urlOfYtGetFunc, (response) => {
    const chunks = []
    response.on('data', (d) => {
      chunks.push(d)
    })

    // Parsing the chunks
    response.on('end', () => {
      resultOfYtGetFunc = JSON.parse((Buffer.concat(chunks).toString()))
      // console.log(resultOfYtGetFunc)

      // Extracting useful data, and allocating it.
      for (i = 0; i < (resultOfYtGetFunc.items).length; i++) {
        extractedResultOfYtGetFunc.push(resultOfYtGetFunc.items[i].id.videoId);
        // console.log(extractedResultOfYtGetFunc);
      }

      callback (null, extractedResultOfYtGetFunc); // move the callback here
    })  
  })
  // callback (null, extractedResultOfYtGetFunc);
}

---

EDIT

You will need to add 1 more parameter in the callback function to receive the error, if any. ytQueryAppJs = httpsYtGetFunc(query, (err, ytQueryAppJs) => {

Answer 2

I'm not Node.js developer but I belive that callback (null, extractedResultOfYtGetFunc); need to be called in http.get callback function.

EDITED move to response.on('end' callback

Something like that:

function httpsYtGetFunc(queryOfYtGetFunc, callback) {
  apiKey = "AI...MI"
  urlOfYtGetFunc = "https://www.googleapis.com/youtube/v3/search?key=" + apiKey + "&part=snippet&q=" + queryOfYtGetFunc + "&maxResults=4&order=relevance&type=video";

  // GETting data and storing it in chunks.
  https.get(urlOfYtGetFunc, (response) => {
    const chunks = []
    response.on('data', (d) => {
      chunks.push(d)
    })

    // Parsing the chunks
    response.on('end', () => {
      resultOfYtGetFunc = JSON.parse((Buffer.concat(chunks).toString()))
      // console.log(resultOfYtGetFunc)

      // Extracting useful data, and allocating it.
      for (i = 0; i < (resultOfYtGetFunc.items).length; i++) {
        extractedResultOfYtGetFunc.push(resultOfYtGetFunc.items[i].id.videoId);
        // console.log(extractedResultOfYtGetFunc);
      }
      callback (null, extractedResultOfYtGetFunc);
    })
  })
}