Confused from array fill results

Question

Can someone explain or tell me why the output
Of this code:

let input = "3x7";
let [rows, cols] = input.split(/x/i).map(v=>parseInt(v))
let matrix = new Array(rows).fill(new Array(cols).fill(0))
matrix[0][0] = 2
console.log(matrix)

Is:

[ [ 2, 0, 0, 0, 0, 0, 0 ],
[ 2, 0, 0, 0, 0, 0, 0 ],
[ 2, 0, 0, 0, 0, 0, 0 ] ]

Answer 1

matrix[0], matrix[1] and matrix[2] are pointing to the same array (new Array(cols). fill(0l), thus it would be the same values for matrix[0][1], matrix[0][2] and matrix[0][2]