Why does the new array change when modifing the old array which itself is inside an array

Question

why does tempArr here give the same value as the one inside the original array

let arr = [[1,2,3,4,5], [6,7,8,9,0]]
let tempArr = arr[0]
arr[0].push(6)
// tempArr.pop()
console.log("arr",arr )
console.log("tempArr",tempArr )

Output:

arr [ [ 1, 2, 3, 4, 5, 6 ], [ 6, 7, 8, 9, 0 ] ]
tempArr [ 1, 2, 3, 4, 5, 6 ]