Reverse an array in place:
let arr = [1, 2, 3]
arr.reverse()
console.log(arr) // [3, 2, 1]
// To reverse without modifying original
let original = [1, 2, 3]
let reversed = [...original].reverse()
console.log(original) // [1, 2, 3]
console.log(reversed) // [3, 2, 1]
reverse() modifies the original. Spread into a new array first if you need to preserve the original.