What causes the occurrence of "undefined" after multiple iterations of my code?

Question

What causes the occurrence of "undefined" after multiple iterations of my code?

I've encountered a curious issue with the code snippet below. Everything seems to be running smoothly except for one thing - after a few iterations, I start getting "undefined" as an output.

You can test this for yourself by running the code multiple times. Initially, you will see the expected output of three random cities, but at some point, "undefined" will pop up. This usually occurs within less than 10 iterations.

I'm puzzled as to why this is happening. What am I overlooking in my code?

var coolWords = ["Amsterdam", "Berlin", "Sofia", "Prague", "Lisbon", "London", "Malaga", "Copenhagen", "Milan"];
    
var newList = [];
    
function niceTripleCombo(coolWords) {
  for (let i = 0; i < 3; i++) {
    var combo = coolWords[Math.floor(Math.random()*coolWords.length)];
    newList.push(" " + combo);
  };
};
    
function iterator(x) {
  if (newList[0] !== newList[1] && newList[1] !== newList[2] && newList[1] !== newList[3]) {
    return newList;
  } else {
    return niceTripleCombo(coolWords);
  }
};
    
    console.log(iterator(niceTripleCombo(coolWords)));

javascript for-loop undefined

Answer 1

Answer №1

Let's examine this test scenario.

Initially, the function

iterator(niceTripleCombo(coolWords))

is invoked by calling console.log().

Next, the function niceTripleCombo(coolWords) will be executed.

Commencement of niceTripleCombo(coolWords)

Within the for loop,

When i = 0, let's assume we receive newList = [" Milan"]

When i = 1, let's assume we receive newList = [" Milan", " London"]

When i = 2, let's assume we receive

newList =  [" Milan", " London", " London"]

Conclusion of niceTripleCombo(coolWords)

Ultimately, we end up with Milan, London, London

Now in the function iterator(),

Due to having 2 instances of London, the if condition will fail, triggering the else block.

First issue arises here, you forgot to initialize the newList as empty. Consequently, upon running niceTripleCombo again, it will append three more cities.

For instance, you might end up with

[" Milan", " London", " London", " Amsterdam", " Malaga", " Sofia"]

Secondly, the statement

return niceTripleCombo(coolWords);

will not yield any result.

The reason for the absence of a return value is that you are returning a function [niceTripleCombo(coolWords)] which itself lacks a return statement.

Your function should either return a value or if returning a function, that function must return a value. In your case, the function niceTripleCombo(coolWords) lacks a return statement and by default, a JavaScript function returns undefined if no other value is specified.

This explains why you are receiving undefined as output.

To rectify this, adjust the else block in your iterator like this:

else {
  newList = [];
  niceTripleCombo(coolWords);
  return iterator();
}

With this modification, you should no longer encounter undefined. Additionally, there is no necessity to pass niceTripleCombo to iterator since the former is not utilized within the latter.

For further information on return, refer to MDN: return statement

Answer 2

Let's examine this test scenario.

Initially, the function

iterator(niceTripleCombo(coolWords))

is invoked by calling console.log().

Next, the function niceTripleCombo(coolWords) will be executed.

Commencement of niceTripleCombo(coolWords)

Within the for loop,

When i = 0, let's assume we receive newList = [" Milan"]

When i = 1, let's assume we receive newList = [" Milan", " London"]

When i = 2, let's assume we receive

newList =  [" Milan", " London", " London"]

Conclusion of niceTripleCombo(coolWords)

Ultimately, we end up with Milan, London, London

Now in the function iterator(),

Due to having 2 instances of London, the if condition will fail, triggering the else block.

First issue arises here, you forgot to initialize the newList as empty. Consequently, upon running niceTripleCombo again, it will append three more cities.

For instance, you might end up with

[" Milan", " London", " London", " Amsterdam", " Malaga", " Sofia"]

Secondly, the statement

return niceTripleCombo(coolWords);

will not yield any result.

The reason for the absence of a return value is that you are returning a function [niceTripleCombo(coolWords)] which itself lacks a return statement.

Your function should either return a value or if returning a function, that function must return a value. In your case, the function niceTripleCombo(coolWords) lacks a return statement and by default, a JavaScript function returns undefined if no other value is specified.

This explains why you are receiving undefined as output.

To rectify this, adjust the else block in your iterator like this:

else {
  newList = [];
  niceTripleCombo(coolWords);
  return iterator();
}

With this modification, you should no longer encounter undefined. Additionally, there is no necessity to pass niceTripleCombo to iterator since the former is not utilized within the latter.

For further information on return, refer to MDN: return statement

Answer 3

Answer №2

Imagine your newList Array contains the following values:

 [" Paris", " Paris", " Rome"]

or a similar scenario where one of the array elements is the same. In this case, when your iterator encounters a repeated element, the if condition fails and then you inadvertently execute

niceTripleCombo(coolWords)

However, this function does not have a return value, resulting in an undefined output.

Answer 4

Imagine your newList Array contains the following values:

 [" Paris", " Paris", " Rome"]

or a similar scenario where one of the array elements is the same. In this case, when your iterator encounters a repeated element, the if condition fails and then you inadvertently execute

niceTripleCombo(coolWords)

However, this function does not have a return value, resulting in an undefined output.

Answer 5

Answer №3

Some pointers to consider regarding your code:

You are not iterating over anything, you are simply checking once.
If your goal is to obtain a unique trio of words, the current method may waste a lot of processing cycles if the randomizer does not generate the desired numbers.
If you are passing an array around, there is no need to make it a global variable. This approach renders your iterator redundant.
Your guessing function lacks a return value, resulting in it returning undefined.

Here's my suggestion:

var coolWords = ["Amsterdam", "Berlin", "Sofia", "Prague", "Lisbon", "London", "Malaga", "Copenhagen", "Milan"];

function niceTripleCombo( list ) {

  // Create a copy of the list to avoid modifying the original.
  let words = list.slice();
  let result = [];
  
  for( let i = 0; i < 3; i++ ){
    
    // Utilize splice to extract a word from the copied array
    // This also removes the word from the array,
    // preventing it from being selected again.
    result.push(
      words.splice( Math.floor( Math.random() * words.length ), 1 )[ 0 ]
    );
    
  }
  
  return result;
  
};

console.log( niceTripleCombo(coolWords) );

This approach ensures the return of a list containing three unique words. It achieves this by selecting a random word from the array, removing it, and adding it to the result. This process repeats with a shortened array, minimizing the needed cycles to only three iterations, regardless of the randomizer's behavior.

Answer 6

Some pointers to consider regarding your code:

You are not iterating over anything, you are simply checking once.
If your goal is to obtain a unique trio of words, the current method may waste a lot of processing cycles if the randomizer does not generate the desired numbers.
If you are passing an array around, there is no need to make it a global variable. This approach renders your iterator redundant.
Your guessing function lacks a return value, resulting in it returning undefined.

Here's my suggestion:

var coolWords = ["Amsterdam", "Berlin", "Sofia", "Prague", "Lisbon", "London", "Malaga", "Copenhagen", "Milan"];

function niceTripleCombo( list ) {

  // Create a copy of the list to avoid modifying the original.
  let words = list.slice();
  let result = [];
  
  for( let i = 0; i < 3; i++ ){
    
    // Utilize splice to extract a word from the copied array
    // This also removes the word from the array,
    // preventing it from being selected again.
    result.push(
      words.splice( Math.floor( Math.random() * words.length ), 1 )[ 0 ]
    );
    
  }
  
  return result;
  
};

console.log( niceTripleCombo(coolWords) );

This approach ensures the return of a list containing three unique words. It achieves this by selecting a random word from the array, removing it, and adding it to the result. This process repeats with a shortened array, minimizing the needed cycles to only three iterations, regardless of the randomizer's behavior.

Answer 7

Answer №4

newList array must be returned within the niceTripleCombo function.

var citiesList = ["Tokyo", "Sydney", "Dubai", "Paris", "Rome", "Moscow", "New York", "Rio de Janeiro", "Los Angeles"];

var newList = [];

function niceTripleCombo(citiesList) {
  newList.length = 0; // Clear the array before starting
  for (let i = 0; i < 3; i++) {
    var combination = citiesList[Math.floor(Math.random()*citiesList.length)];
    newList.push(" " + combination);
  };
  return newList; //Returning an array.
};

function checkDuplicates(x) {
  if (newList[0] !== newList[1] && newList[1] !== newList[2] && newList[1] !== newList[3]) {
    return newList;
  } else {
    return niceTripleCombo(citiesList);
  }
};

console.log(checkDuplicates(niceTripleCombo(citiesList)));

Answer 8

newList array must be returned within the niceTripleCombo function.

var citiesList = ["Tokyo", "Sydney", "Dubai", "Paris", "Rome", "Moscow", "New York", "Rio de Janeiro", "Los Angeles"];

var newList = [];

function niceTripleCombo(citiesList) {
  newList.length = 0; // Clear the array before starting
  for (let i = 0; i < 3; i++) {
    var combination = citiesList[Math.floor(Math.random()*citiesList.length)];
    newList.push(" " + combination);
  };
  return newList; //Returning an array.
};

function checkDuplicates(x) {
  if (newList[0] !== newList[1] && newList[1] !== newList[2] && newList[1] !== newList[3]) {
    return newList;
  } else {
    return niceTripleCombo(citiesList);
  }
};

console.log(checkDuplicates(niceTripleCombo(citiesList)));

What causes the occurrence of "undefined" after multiple iterations of my code?

Answer №1

Answer №2

Answer №3

Answer №4

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