push() method not working properly in JavaScript - Stack Overflow

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I'm trying to write a quite simple program that divides an array in another array of defined size smaller arrays, however the push() method is not working. Could someone please help me with it?

function chunk(array, size) {
  var newArray = [];
  var tempArray = [];

  for (let i = 0; i < array.length / size; i++) {
    for (let j = size * i, k = 0; j < size * i + size; j++, k++)
      tempArray[k] = array[j];

    newArray.push(tempArray);
  }

  return newArray;
}

var data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2));

The ideal output should be [[1, 2],[3, 4], [5, 6], [7, 8]]. However im getting [[7,8],[7,8],[7,8],[7,8]].

I'm trying to write a quite simple program that divides an array in another array of defined size smaller arrays, however the push() method is not working. Could someone please help me with it?

function chunk(array, size) {
  var newArray = [];
  var tempArray = [];

  for (let i = 0; i < array.length / size; i++) {
    for (let j = size * i, k = 0; j < size * i + size; j++, k++)
      tempArray[k] = array[j];

    newArray.push(tempArray);
  }

  return newArray;
}

var data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2));

The ideal output should be [[1, 2],[3, 4], [5, 6], [7, 8]]. However im getting [[7,8],[7,8],[7,8],[7,8]].

• javascript
• array-push

Share Improve this question Follow edited Aug 15, 2021 at 16:42 Behemoth 9,40055 gold badges2727 silver badges4848 bronze badges asked Aug 3, 2021 at 6:16 Alonso MarañónAlonso Marañón 5133 bronze badges 2

• 2 move var tempArray = []; inside of your first for loop. Currently, you're pushing the same array reference each time, and so modifications to it will impact it within your array – Nick Parsons Commented Aug 3, 2021 at 6:21
• 1 You are creating only one temparray in he very beginning and then overwriting its elements and pushing the same array multiple times – derpirscher Commented Aug 3, 2021 at 6:22

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3 Answers 3

Sorted by: Reset to default 6

You're almost there. Just move the tempArray definition inside your first for-loop. Otherwise you would be pushing the same array each time.

Working Example:

function chunk(array, size) {
  const newArray = [];

  for (let i = 0; i < array.length / size; i++) {
    const tempArray = [];
    for (let j = size * i, k = 0; j < size * i + size; j++, k++)
      tempArray[k] = array[j];

    newArray.push(tempArray);
  }

  return newArray;
};

const data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2)); // [[1, 2],[3, 4], [5, 6], [7, 8]]

@Behemoth's answer is the correct one for the question. But if you want, you can take a slightly different approach like this to reach the solution as well.

function chunk(array, size){
    const newArray = [];
    let i,j;
    
    for (i = 0,j = array.length; i < j; i += size) {
      newArray.push(array.slice(i, i + size));
    }
    return newArray;
};

var data = [1, 2, 3, 4, 5, 6, 7 ,8];

console.log(chunk(data, 2));

Slightly different solution than @Behemoth and @Rukshan

function chunk(array, size) {
  var newArray = [];
  var tempArray = [];

  for (let i = 0; i < array.length / size; i++) {

    for (let j = i; j < i + 1; j++) {
      for (let k = 0; k < size; k++) {
        if (array[size * j + k]) {
          tempArray.push(array[size * j + k]);
        }
      }
      newArray.push(tempArray);
      tempArray = [];
    }
  }
  return newArray;
};

var data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2));

The solution would be [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9 ] ] instead of [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ]]

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