Curriculum array output problem

JavaScript
1

Tell us what’s happening:
Why output is:
[ [ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ] ]
instead:
[ [ 0, 0 ],
[ 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ] ]

Your code so far


function zeroArray(m, n) {
// Creates a 2-D array with m rows and n columns of zeroes
let newArray = [];
let row = [];
for (let i = 0; i < m; i++) {
  // Adds the m-th row into newArray

  for (let j = 0; j < n; j++) {
    // Pushes n zeroes into the current row to create the columns
    row.push(0);
  
  }
  // Pushes the current row, which now has n zeroes in it, to the array
  newArray.push(row);
}
return newArray;
}

let matrix = zeroArray(3, 2);
console.log(matrix);

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Challenge: Use Caution When Reinitializing Variables Inside a Loop

Link to the challenge:

2

here a reference to row is added to newArray, not a copy
so at the end you have
[ row, row, row ], whatever the row array looks like

3

i still don’t understand, when i = 0 I am only pushing 2 zeros to newArray, when i = 1 I am pushing 4 zeros…

4

it means that when i = 1 and I use newArray.push(row), I am updating row that I pushed when i was equal to 0?

5

try following this:

let arr = [0,0,0]
let outerArr = [];

outerArr.push(arr)
// outerArr equals [[0,0,0]]

arr[1] = 1;
// arr is equal [0,1,0]
// and outerArr is also equal to [[0,1,0]]
outerArr.push(arr)
// now outerArr is equal [[0,1,0], [0,1,0]]

because arrays work by reference, doing outerArr.push(arr) you are pushing a reference to arr, aby change to arr is reflected in outerArr because outerArr is practically [arr, arr]