❗️Что будет на выходе?

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
  [10, , ],
];

let flattenedMatrix = [];

for (let i = 0; i < matrix.length; i++) {
  for (let j = 0; j < matrix[i].length; j++) {
    flattenedMatrix.push(matrix[i][j]);
  }
}

console.log(flattenedMatrix);

Ответ: 11
[ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, undefined ]

JavaScript test | #JavaScript