var head = [1, 2, 3, 4, 5] function arrayToListNode(arr) { if (arr.length === 0) return null; let head = { val: arr[0], next: null } let pre = head; for (let i = 1; i < arr.length; i++) { pre.next = { val: arr[i], next: null } pre = pre.next // let node = { val: arr[i], next: null } // pre.next = node; // pre = node } return head } head = arrayToListNode(head) console.log('head', head)