How do arrays and linked lists differ?

The difference is memory layout. An array reserves a contiguous block, so the address of any element can be computed directly. A linked list scatters nodes and connects them with references, so reaching a position requires walking from the head.

class ListNode {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

function prepend(head, value) {
  const node = new ListNode(value);
  node.next = head;
  return node;
}

The practical comparison

• Array access by index is O(1); linked list access is O(n)
• Inserting at the front of an array is O(n); prepending a node is O(1)
• Arrays have better cache locality because elements are contiguous
• Linked lists need extra memory for pointers
• Deleting a node from a linked list is O(1) if you already hold the previous node

In JavaScript, arrays are dynamic and usually the right default. Linked lists matter when you are constantly splicing at known positions, implementing a queue with O(1) removal, or building structures where node identity is useful.