Encountering an "UNDEFINED" result after executing a basic for loop in a beginner's JavaScript program

Question

Encountering an "UNDEFINED" result after executing a basic for loop in a beginner's JavaScript program

function reverseArrayItems(arr) {
  for (let i = arr.length - 1; i >= 0; i--) {
    console.log(`${arr[i]}`);
  }
};

const words = ['reversed', 'be', 'should', 'order', 'The'];

console.log(reverseArrayItems(words))

// Expected output: ['The', 'order', 'should', 'be', 'reversed'];

const numbers = [10, 20, 30, 40, 50];

console.log(reverseArrayItems(numbers));

// Expected output: 50, 40, 30, 20, 10

I keep getting an undefined at the end. Can someone help me out with this small problem? Apologies for the beginner question.

javascript loops

Answer 1

Answer №1

The reason it ends up printing undefined is because attempting to console.log the function does not generate any output, as the function itself does not return anything. In this case, you could simply call the function without using console.log.

reverseArray(sentence)
reverseArray(nums)

An alternative method for reversing an array is to utilize the built-in function reverse(). You can modify your function like so:

const reverseArray = (words) => {
  words.reverse().forEach(item => {
    console.log(item);
  });
};

Answer 2

The reason it ends up printing undefined is because attempting to console.log the function does not generate any output, as the function itself does not return anything. In this case, you could simply call the function without using console.log.

reverseArray(sentence)
reverseArray(nums)

An alternative method for reversing an array is to utilize the built-in function reverse(). You can modify your function like so:

const reverseArray = (words) => {
  words.reverse().forEach(item => {
    console.log(item);
  });
};

Answer 3

Answer №2

The issue arises when the function does not have a return statement, causing it to return nothing, resulting in undefined. Therefore, your

console.log(reverseArray(sentence))

call is essentially equivalent to console.log(undefined).

This solution addresses the problem by ensuring that the function correctly returns the reversed array.

const reverseArray = (words) => {
  let reversed = [];
  for (let i = words.length - 1; i >= 0; i--) {
     reversed.push(words[i]);
  }
  return reversed;
};

const sentence = ['sense.', 'make', 'all', 'will', 'This'];

console.log(reverseArray(sentence));

// The output should be ['This', 'will', 'all', 'make', 'sense.'];

const nums = [1, 2, 3, 4, 5];

console.log(reverseArray(nums));

Answer 4

The issue arises when the function does not have a return statement, causing it to return nothing, resulting in undefined. Therefore, your

console.log(reverseArray(sentence))

call is essentially equivalent to console.log(undefined).

This solution addresses the problem by ensuring that the function correctly returns the reversed array.

const reverseArray = (words) => {
  let reversed = [];
  for (let i = words.length - 1; i >= 0; i--) {
     reversed.push(words[i]);
  }
  return reversed;
};

const sentence = ['sense.', 'make', 'all', 'will', 'This'];

console.log(reverseArray(sentence));

// The output should be ['This', 'will', 'all', 'make', 'sense.'];

const nums = [1, 2, 3, 4, 5];

console.log(reverseArray(nums));

Answer 5

Answer №3

It seems like your reverseArray function isn't providing any output, resulting in an undefined response.

The array is not being reversed or saved anywhere within the function.

To fix this issue, you should reverse the array and store it in a variable before returning it at the end of the function.

Alternatively, consider using the built-in string.reverse() method for a quicker solution!

Answer 6

It seems like your reverseArray function isn't providing any output, resulting in an undefined response.

The array is not being reversed or saved anywhere within the function.

To fix this issue, you should reverse the array and store it in a variable before returning it at the end of the function.

Alternatively, consider using the built-in string.reverse() method for a quicker solution!

Answer 7

Answer №4

If you don't explicitly return a value from a JavaScript function, it will default to returning undefined.

Check out this example:

const capitalizeWords = (words) => {
  for (let word of words) {
     console.log(`${word.toUpperCase()}`);
  }
  return "" //Magic happens here
};

const phrase = ['hello', 'world', 'of', 'coding'];

console.log(capitalizeWords(phrase))

// Expected output: ['HELLO', 'WORLD', 'OF', 'CODING']

const numbers = [10, 20, 30, 40, 50];

console.log(capitalizeWords(numbers));

Answer 8

If you don't explicitly return a value from a JavaScript function, it will default to returning undefined.

Check out this example:

const capitalizeWords = (words) => {
  for (let word of words) {
     console.log(`${word.toUpperCase()}`);
  }
  return "" //Magic happens here
};

const phrase = ['hello', 'world', 'of', 'coding'];

console.log(capitalizeWords(phrase))

// Expected output: ['HELLO', 'WORLD', 'OF', 'CODING']

const numbers = [10, 20, 30, 40, 50];

console.log(capitalizeWords(numbers));

Encountering an "UNDEFINED" result after executing a basic for loop in a beginner's JavaScript program

Answer №1

Answer №2

Answer №3

Answer №4

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