Implement a Queue in JavaScript

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Implement a Queue in JavaScript

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This is the second of a series of articles on implementing data structures in JavaScript. If you’re new to data structures, be sure to read this introduction (link to come) to data structures first. Already know about queues? Let’s get started on some more advanced data structures like the binary search tree!

A queue is like a line at a restaurant. It’s “first in, first out” (FIFO), which means that the item that was put in the queue longest ago is the first item that comes out. “First come, first served.”

The Problem

Implementing a Queue in JavaScript involves creating a data structure that follows the First-In-First-Out (FIFO) principle. To solve this problem, you need to design a class or a set of functions that provide the necessary operations for a Queue. The Queue should support adding elements to the back (enqueue) and removing elements from the front (dequeue). Additionally, it should allow for inspecting the front element (peek) without removing it. JavaScript provides various approaches to implement a Queue, such as using arrays or linked lists. By breaking down the problem, you can identify key components, such as maintaining a reference to the front and back of the Queue, updating these references when enqueueing or dequeueing elements, and handling edge cases like an empty Queue. The solution to this problem enables JavaScript developers to utilize the Queue data structure for managing ordered collections, scheduling tasks, or solving other problems that require FIFO behavior.

Most use-cases for a queue are involved with building or utilizing other data structures. One example could be in breadth-first traversal of a tree.

Methods of a Queue

Queues have two main methods:

**enqueue() **: Adds a node (value)
**dequeue() **: Removes and returns the next node in the queue

They can also include other utility methods:

**peek() **: Returns the node at the front of the queue (without removing)
**isEmpty() **: Returns True if the queue is empty, otherwise returns false

Pseudo Code

Create Queue constructor Define storage, count, and lowest count

 Add value to queue
 Increment count

 Save node to delete in var
 Delete node
 Increment lowest count
 Return saved node

 Return count minus lowest count

Time complexity

If you don’t know much about time complexity, you’ll be lost until you read this short article on time complexity in JavaScript. For each method on the queue, the worst-case time complexity is constant — O(1). This means that as the stack grows to n size, each method completes its job in the same amount of time.

enqueue: Constant — O(1)
dequeue: Constant — O(1)

Code

peek: Constant — O(1)
isEmpty: Constant — O(1)

Are you ready to take on some more advanced data structures? Next up is the binary search tree!

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Having worked across sites raking in over 50 billion website visits annually with Higglo Digital I write about tech topics and teach…