```js
var Node = function(data, prev) {
this.data = data;
this.prev = prev;
this.next = null;
};
var DoublyLinkedList = function() {
this.head = null;
this.tail = null;
// change code below this line
// change code above this line
};
```
### After Test
```js
console.info('after the test');
```
## Solution