JS Practice — Built-in Objects

Array.prototype.copyWithin() — negative target index

📖 Usage Example

const arr = [1, 2, 3, 4, 5]
arr.copyWithin(-2, 0, 2)  // → [1, 2, 3, 1, 2]
// uses negative target index

Use negative indices with copyWithin() to reference positions from the end of the array.

Array.prototype.copyWithin() — negative indices

Like other array methods, copyWithin supports negative indices. copyWithin(-1, 0, 1) copies the first element to the last position.

Challenge: Implement copyToEnd(arr) that copies the first element to the last position using arr.copyWithin(-1, 0, 1).

copyToEnd([1, 2, 3, 4]) // → [1, 2, 3, 1]
copyToEnd([9, 0, 0])    // → [9, 0, 9]

💡 Hints (2)