链表反转

const head = {
  'val':5,
  'next':{
      'val':4,
      'next':{
          'val':3,
          'next':{
              'val':2,
              'next':{
                  'val':1,
                  'next':undefined
              }
          }
      }
  }
}

var reverseList = function (node) {
    let pre = null
    while(node){
        let next = node.next

        node.next = pre
        pre = node

        node = next
    }
}

console.log(reverseList(head))