let matrix = [
  [0,0,0,0,0],
  [0,0,0,0,0],
  [0,0,0,0,0],
  [0,0,0,0,0],
]
// copies just values, not references!
function getCopyOfMatrix(mat) {
  return JSON.parse(JSON.stringify(mat))
}

let copyOfMatrix = getCopyOfMatrix(matrix);