Simple JavaScript solution [87%, 50%]
Runtime: 80 ms, faster than 87.16% of JavaScript online submissions for Reorder List.\nMemory Usage: 41.8 MB, less than 50.00% of JavaScript online submissions 
Runtime: 80 ms, faster than 87.16% of JavaScript online submissions for Reorder List.\nMemory Usage: 41.8 MB, less than 50.00% of JavaScript online submissions for Reorder List.\n```\nfunction reorderList(head) {\n  const arr = [];\n  let index = head;\n  \n  while (index) {\n    arr.push(index);\n    index = index.next;\n  }\n\n  for (let l = 0; l < arr.length; l++) {\n    let r = arr.length - 1 - l;\n    if (l >= r) { arr[l].next = null; break; }\n    arr[l].next = arr[r];\n    arr[r].next = arr[l + 1];\n  }\n}\n```
['JavaScript']