Accept array, convert it into linked list and return list head

algo-build-linked-list-from-array

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

function createList(arr){
  let result = arr.map((item, index, arr)=>{
    const node = new ListNode(item)
    return node
  })

  result = result.map((item, index, arr)=>{
    if(index < (arr.length-1)){
      item.next = arr[index+1]
    }
    return item
  })

  return result[0]
}