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Design Patterns in JavaScript: A Comprehensive Guide

Tope Fasasi on December 25, 2023

JavaScript, with its widespread adoption and versatility, has become a cornerstone of modern web development. As you delve deeper into JavaScript d...

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Valery Zinchenko • Dec 26 '23

That's not just JS patterns, it's widely known Gang of Four Patterns.
en.m.wikipedia.org/wiki/Design_Pat...

If you want to know more about Software Design:
en.m.wikipedia.org/wiki/Software_d...
Comprehensive read about System design patterns:
en.m.wikipedia.org/wiki/Category:S...

There is only one downgrade in Wikipedia, the language may be complicated to understand.

raydot • Dec 27 '23

I came here to say this exact same thing. These are the typical GoF patterns.

db325 • Dec 26 '23

Thank you, this found me right in time. I live the way you break down reach pattern and explain the use case asking with the example. This is by far one of the most helpful articles I've read all year!

Andy Edwards • Dec 26 '23 • Edited

The singleton example isn’t very idiomatic JS if you ask me…it seems like you were thinking within the conventions of some other language you’re experienced in rather than a natural way of doing things in JS. Two calls to new returning the same object is very very unusual behavior, thus a nasty surprise. JS programmers I know just export a const, or a getter function that returns the same value.

Dev Geos • Dec 28 '23

I also found this strange but good to know as possibility.

Thiago Marques • Dec 26 '23

The example of Bridge Pattern is not printing the colors as expected.

Julio • Jan 1

I resolved this by invoking the getColor() method for each Color class implementor object:

const redColor = new RedColor().getColor();
const redCircle = new Circle(redColor);
redCircle.draw(); // Output: "Drawing a red circle"

const blueColor = new BlueColor().getColor();
const blueSquare = new Square(blueColor);
blueSquare.draw(); // Output: "Drawing a blue square"

Alex • Jan 8

As already pointed out, these are GoF or general OOP patterns. What I would also like to point out, that -at least for me- this ist not how you would solve the underlying problems in JS / TS, as it's not inherently an OOP language, but a prototype-based language with first-class functions, it's unique way of what you can do with objects and the way the module-system works. For example:

Singleton Pattern
Moules are effectively singletons, so no need to use any other pattern

// module.js
let foo = 'bar';
const singleton = {
  foo,
  logFoo: () => console.log(foo),
}

export const singleton;

// main.js
import {singleton} from './module.js'

singleton.foo = 'baz'; // changed for all uses of "singleton"
singleton.logFoo() // -> 'baz'

// main2.js
import {singleton} from './module.js'
singleton.logFoo() // -> 'baz'

Generally I rarely use classes at all, instead I usually use (typed) objects. My favorite example is the Command pattern.

Command Pattern
This example also uses TypeScript to make sure a command always looks the same. You could also use it with vanilla JS and manually assert command objects always having the same fields. I also added a simple logic to implement undoing commands which in my opinion is one of the biggest real-world strengths / use-cases of this pattern.

type UndoFn<T> = (args: T) => void;

interface Command<T> {
  execute: (args: T) => UndoFn<T>;
}

const logMessageCmd: Command<string> = {
  execute: (msg) => {
    console.log('Message:', msg);
    return () => console.log('Revoked message', msg);
  }
}

const undo = logMessageCmd.execute('Hello World'); // -> 'Message: Hello World'
undo(); // 'Revoked message: Hello World'

Nathan Hedglin • Dec 27 '23

Seems like a copy paste from other articles.

"Mediator patterns are a type of behavioral design pattern that define an object that acts as a central hub for coordinating the interactions between a group of objects. The mediator encapsulates the logic and rules for how the objects should communicate, and reduces the coupling between them. The objects only need to know about the mediator, and not about each other. This simplifies the object interfaces and promotes modularity and reusability."

https://www.linkedin.com/advice/how-can-you-coordinate-object-interactions?utm_source=share&utm_medium=member_android&utm_campaign=share_via

Mauricia Ragland • Jan 4 • Edited

Great article. I've been doing this for so long that sometimes I forget which patterns I'm using.

The Colleague class in the Mediator example does not look like it will work if colleague2 sends a message.

Your mediator would benefit from a generic send that can determine which objects receive the message:

class Mediator {
    sendMessage(message, sender) {
        for (const colleague of this.colleagues) {
            if (colleague !== sender) {
                colleague.receive(message);
            }
        }
    }
}
class Colleague {
    send(message) {
        this.mediator.sendMessage(message, this);
    }
}

Thanks for this post!

Rommel C. Manalo • Dec 28 '23 • Edited

The title "JS Design Patterns" is misleading, it is not specific to JS. Most programming language that uses OOP can do that. You just write the example in JS.

I think it better to title as Design Patterns with JS examples..

Changwoo Yoo • Jan 3

I'm not sure but it seems like using ChatGPT to write this article 😂

Bridger Brown • Dec 27 '23

Thats a lot of patterns to read, bookmarking lol

Raí B. Toffoletto • Dec 29 '23

And... you can achieve all of those without using the word CLASS in JS. 😉

codepraycode • Jan 1

Thank you for this

James Auble • Jan 13

Like all too often on dev.to, I think the comments of this article are more helpful and educational than the article itself.

wakywayne • Dec 31 '23

Why does he not need to call super() in the bridge patter example?

wakywayne • Dec 28 '23

God tier article

Dev Geos • Dec 28 '23

I found your post useful even if using of some models is not recommended in JS.
Thanks ! :)

vanbeonhv • Feb 28

I don't think using js class as example for design pattern is a good thing.
after taking a glance at first example. I think I can't get it and apply to my current work