Use Caution When Reinitializing Variables Inside a Loop

JavaScript
1 
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);

How come the code that is given originally on this challenge leads to a result of
[ [ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ] ]
instead of
[ [ 0, 0, ],
[ 0, 0, 0, 0,],
[ 0, 0, 0, 0, 0, 0 ] ]
?

2

Because every array representing a row is the exact same array.

3

Yeah but the first time the row array gets pushed in it´s value is [0, 0], but the second time it gets pushed in it´s value now is [0, 0, 0, 0], why doesn´t the first array that got pushed in stay as [0, 0]? Does it somehow automatically update whenever the row array gets updated?

4

Pushing doesn’t keep it from being the exact same array. Everywhere you use that exact same array you will see the changes to that array

5

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