7 best JavaScript Design Patterns You Should Know

7 best JavaScript Design Patterns You Should Know

7 best JavaScript Design Patterns You Should Know - Design patterns in JavaScript are reusable solutions applied to commonly occurring problems in writing JavaScript web applications.

7 best JavaScript Design Patterns You Should Know - Design patterns in JavaScript are reusable solutions applied to commonly occurring problems in writing JavaScript web applications.


It is quite appropriate to refer JavaScript design patterns as templates to provide solutions to problems but not quite to say that these patterns can replace the developers.

Design patterns help combine experiences of many developers to structure the codes in an optimized manner that meet the problems we are seeking solutions to, and gives common vocabulary used to describe solutions to our problems than describing the syntax and semantics of our code.

JavaScript design patterns assist developers to write organized, beautiful and well-structured codes. Although design patterns, when used can easily be re-used, they can never supplement developers, rather they only support them by preventing minor issues that could lead to major problems on the web application development by providing generalized solutions that are not tied to a specific problem.

They decrease the overall codebase by doing away with unnecessary repetitions, thus makes our code more robust than the ad-hoc solutions.

In this article, I will explore seven best and most popular JavaScript design patterns, which of course most of them will fall under three categories namely; creation design patterns, structural design patterns and behavioral design patterns. A pattern is something like the following image; just to acquaint you into the context.

** **

1. Constructor Design Pattern.

This is a special method that is used to initialize the newly created objects once a memory is allocated. Since JavaScript is typically object-oriented, it deals with objects most, therefore I intend to delve in to object constructors. There are three ways to create new objects in JavaScript:

The following is one way to create a constructor design pattern.

// This creates a new empty Object

var newObject = {};

// This creates a new empty Object

var newObject = Object.create(Object.prototype);

var newObject = newObject();

To access the properties of a function, you need to initialize the object.

const object = new ConstructorObject();

Whereby the new keyword above tells JavaScript that aconstructorObjectshould act as a constructor. Inheritance is one thing this design pattern does not support. Find out more details


2. Prototype Pattern

The prototype pattern is based on prototypical inheritance whereby objects created to act as prototypes for other objects. In reality, prototypes act as a blueprint for each object constructor created.


var myCat= {
name:"Ford Escort",
console.log("Stop! I am applying brakes");
Panic : function (){
console.log ( "wait. how do you stop thuis thing?")
// use objec create to instansiate a new car
var yourCar= object.create(myCar);
//You can now see that one is a prototype of the other
console.log (yourCar.name);]

3. Module Design Pattern

In the module design pattern, there is an improvement from the prototype pattern. The different types of modifiers (both private and public) are set in the module pattern. You can create similar functions or properties without conflicts. There is the flexibility of renaming functions publicly. The daunting part of this is the inability to override the created functions from the outside environment.


function AnimalContainter () {

const container = [];

function addAnimal (name) {

function getAllAnimals() {
return container;

function removeAnimal(name) {
const index = container.indexOf(name);
if(index < 1) {
throw new Error('Animal not found in container');
container.splice(index, 1)

return {
add: addAnimal,
get: getAllAnimals,
remove: removeAnimal

const container = AnimalContainter();

console.log(container.get()) //Array(3) ["Hen", "Goat", "Sheep"]
console.log(container.get()); //Array(2) ["Hen", "Goat"]

4. Singleton Pattern

It is essential in a scenario where only one instance needs to be created, for example, a database connection. It is only possible to create an instance when the connection is closed or you make sure to close the open instance before opening a new one. This pattern is also referred to as strict pattern, one drawback associated with this pattern is its daunting experience in testing because of its hidden dependencies objects which are not easily singled out for testing.


function DatabaseConnection () {

let databaseInstance = null;

// tracks the number of instances created at a certain time
let count = 0;

function init() {
console.log(`Opening database #${count + 1}`);
//now perform operation
function createIntance() {
if(databaseInstance == null) {
databaseInstance = init();
return databaseInstance;
function closeIntance() {
console.log('closing database');
databaseInstance = null;
return {
open: createIntance,
close: closeIntance

const database = DatabseConnection();
database.open(); //Open database #1
database.open(); //Open database #1
database.open(); //Open database #1
database.close(); //close database

5. Factory Pattern.

It is a creational concerned with the creation of objects without the need for a constructor. It provides a generic interface for creating objects, where we can specify the type of factory objects to be created. Therefore, we only specify the object and the factory instantiates and returns it for us to use. It is wise for us to use factory pattern when the object component set up has a high level of complexity and when we want to create different instances of objects easily depending on the environment we are in. We can also use factory pattern when working with many small objects sharing the same properties and when composing objects that need decoupling.


// Dealer A

DealerA = {};

DealerA.title = function title() {
return "Dealer A";

DealerA.pay = function pay(amount) {
`set up configuration using username: ${this.username} and password: ${
return `Payment for service ${amount} is successful using ${this.title()}`;

//Dealer B

DealerB = {};
DealerB.title = function title() {
return "Dealer B";

DealerB.pay = function pay(amount) {
`set up configuration using username: ${this.username}
and password: ${this.password}`
return `Payment for service ${amount} is successful using ${this.title()}`;

//@param {*} DealerOption
//@param {*} config

function DealerFactory(DealerOption, config = {}) {
const dealer = Object.create(dealerOption);
Object.assign(dealer, config);
return dealer;

const dealerFactory = DealerFactory(DealerA, {
username: "user",
password: "pass"

const dealerFactory2 = DealerFactory(DealerB, {
username: "user2",
password: "pass2"

6. Observer Pattern

The observer design pattern is handy in a place where objects communicate with other sets of objects simultaneously. In this observer pattern, there is no unnecessary push and pull of events across the states, rather the modules involved only modify the current state of data.


function Observer() {
this.observerContainer = [];

Observer.prototype.subscribe = function (element) {

// the following removes an element from the container

Observer.prototype.unsubscribe = function (element) {

const elementIndex = this.observerContainer.indexOf(element);
if (elementIndex > -1) {
this.observerContainer.splice(elementIndex, 1);

* we notify elements added to the container by calling
* each subscribed components added to our container
Observer.prototype.notifyAll = function (element) {
this.observerContainer.forEach(function (observerElement) {

7. Command Pattern

To wrap up, I would say the command design pattern ends my 7 best sums of JavaScript design patterns. The command design pattern encapsulates method invocation, operations or requests into a single object so that we can pass method calls at our discretion. The command design pattern gives us an opportunity to issue commands from anything executing commands and delegates responsibility to different objects instead. These commands are presented in run() and execute() format.


var carManager = {

//information requested
requestInfo: function( model, id ){
return "The information for " + model + " with ID " + id + " is foo bar";

// now purchase the car
buyVehicle: function( model, id ){
return "You have successfully purchased Item " + id + ", a " + model;

// now arrange a viewing
arrangeViewing: function( model, id ){
return "You have successfully booked a viewing of " + model + " ( " + id + " ) ";


It is beneficial for JavaScript developers to use design patterns. Some major advantages of using design patterns include project maintainability and also cuts off unnecessary work on the development cycle. Even though JavaScript design patterns can provide solutions to complex problems, needless to say, rapid development and productivity, it is improper to conclude that these design patterns can replace the developers.

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:


First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?


I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI