JS Practice — Built-in Objects

Array.prototype.copyWithin() — shift elements left

📖 Usage Example

const arr = [1, 2, 3, 4, 5]
arr.copyWithin(0, 3)  // → [4, 5, 3, 4, 5]
// pastes elements at index 3+ to the start

Pass 0 as the target to copyWithin() to shift elements to the beginning of the array.

Array.prototype.copyWithin() — shifting

Copying from index 1 to index 0 effectively shifts elements left by one position. The last element remains unchanged (since the source is one shorter than the target range).

Challenge: Implement shiftLeft(arr) that copies from index 1 to the beginning of the array using arr.copyWithin(0, 1).

shiftLeft([1, 2, 3, 4]) // → [2, 3, 4, 4]
shiftLeft([10, 20, 30]) // → [20, 30, 30]

💡 Hints (2)

• `copyWithin(0, 1)` copies arr[1], arr[2], arr[3]... to positions 0, 1, 2...
• The last element stays because there is no element to copy into its position from the right.