Sth about linkedList in javaScript

linkedList.js

function ListNode(val) {
  this.val = val;
  this.next = null;
}

const last = arr => arr[arr.length - 1];
const head = arr => arr[0];

const linkedListFromArray = array => head(array.reduce((acc, curr, currIdx, arr) => {
  let node = new ListNode(curr);
  if (last(acc)) {
    last(acc).next = node;
  }
  acc.push(node);
  return acc;
}, []));