Implement a queue data structure in JavaScript that contains the following operations:

• new Queue(): Creates an instance of a Queue class that doesn't contain any items. The constructor does not accept any arguments.
• enqueue(item): Adds item to the back of the queue and returns the new number of items. Required time complexity: O(1).
• dequeue(): Removes and returns the item at the front of the queue, or returns undefined if the queue is empty. Required time complexity: O(1).
• isEmpty(): Determines if the queue is empty. Required time complexity: O(1).
• front(): Returns the item at the front of the queue without removing it, or returns undefined if the queue is empty. Required time complexity: O(1).
• back(): Returns the item at the back of the queue without removing it, or returns undefined if the queue is empty. Required time complexity: O(1).
• length(): Returns the number of items in the queue. Required time complexity: O(1).

Examples

const queue = new Queue();
queue.isEmpty(); // true
queue.enqueue(1);
queue.enqueue(2);
queue.length(); // 2
queue.enqueue(3);
queue.front(); // 1
queue.back(); // 3
queue.dequeue(); // 1
queue.isEmpty(); // false