# JavaScript Data Structures: Queue: Recap

4 January 2020

## Intro

Last time, we added the `dequeue`

method.

I hope you learned something about the concept of a Queue and tried your best to implement it on your own.

### Thoughts about the Queue 💭

We implemented the Queue using a Singly Linked List.

The Queue data structure is a very important concept, because we use it all the time.

The Queue is based on the "First In, First Out"-Principle, meaning the first node that goes into the queue will later be the first node, that goes out of the queue.

Examples in real life: people who want to pay in a store, the tasks of a printer.

- Access:
`O(N)`

- Search:
`O(N)`

- Insert:
`O(1)`

- Remove:
`O(1)`

## Final Implementation 📝

Our Queue has these methods:

`enqueue`

, to add a node to the end of the queue`dequeue`

, to remove a node from the start of the queue

```
class Node {
constructor(value) {
this.value = value;
this.next = null;
}
}
class Queue {
constructor() {
this.length = 0;
this.start = null;
this.end = null;
}
enqueue(value) {
const newNode = new Node(value);
if (!this.length) {
this.start = newNode;
this.end = newNode;
} else {
this.end.next = newNode;
this.end = newNode;
}
this.length += 1;
return newNode;
}
dequeue() {
if (!this.length) {
return null;
} else {
const nodeToRemove = this.start;
this.start = this.start.next;
nodeToRemove.next = null;
if (this.length === 1) {
this.end = null;
}
this.length -= 1;
return nodeToRemove;
}
}
}
```

## Further Reading 📖

## Questions ❔

- Can you implement a new method
`peek`

, that returns the start node, without removing it?

## Next Part ➡️

We will compare the Data Structures we've built so far.

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