## Intro

Last time, we learned what a Queue is and set it up.

Today, we learn how to enqueue / add a new node to the end of the Queue.

## Starter Code ▶️

We start with the code from the last part.

``````class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}

class Queue {
constructor() {
this.length = 0;
this.start = null;
this.end = null;
}
}
``````

## Thoughts 💭

First, we should think about the constraints and possibilities:

If the Queue is empty:

• create a new node
• set the new node as start and end
• increase the queue's length by 1
• return the new node

All remaining cases:

• create a new node
• set the new node as the end's next node
• set the new node as the new end
• increase the queue's length by 1
• return the new node

## Example

``````// current queue:
A (start) ==> B (end)

// desired queue:
A (start) ==> B       ==> C (end)
``````

Steps:

``````// current queue:
A (start) ==> B (end)

// set the new node as the end's next node
A (start) ==> B (end) ==> C

// set the new node as the new end
A (start) ==> B       ==> C (end)

// desired queue:
A (start) ==> B       ==> C (end)
``````

## Implementation 📝

``````class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}

class Queue {
constructor() {
this.length = 0;
this.start = null;
this.end = null;
}

enqueue(value) {
// create a new node
const newNode = new Node(value);

if (!this.length) {
// set the new node as start and end
this.start = newNode;
this.end = newNode;
} else {
// set the new node as the end's next node
this.end.next = newNode;
// set the new node as the new end
this.end = newNode;
}

// increase the queue's length by 1
this.length += 1;
// return the new node
return newNode;
}
}
``````

## Result

Let's have a look how to use the `enqueue` method and its results.

``````const newQueue = new Queue();

// empty queue
console.log(newQueue);
// Queue { length: 0, start: null, end: null }

console.log(newQueue.enqueue("new A"));
// Node { value: 'new A', next: null }

// queue with 1 node
console.log(newQueue);
// Queue {
//   length: 1,
//   start: Node { value: 'new A', next: null },
//   end: Node { value: 'new A', next: null }
// }

console.log(newQueue.enqueue("new B"));
// Node { value: 'new B', next: null }

// queue with 2 nodes
console.log(newQueue);
// Queue {
//   length: 2,
//   start: Node { value: 'new A', next: Node { value: 'new B', next: null } },
//   end: Node { value: 'new B', next: null }
// }
``````

## Next Part ➡️

We will implement our next method to `dequeue` the first node.

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## Questions ❔

• Do you see some similarities to the Singly Linked List or Doubly Linked List?