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title	description	published	authors	tags	attached	license
Using JavaScript Classes without the `class` keyword		2023-07-16T21:52:59.284Z	crutchcorn	computer science		cc-by-4

Classes in JavaScript are both powerful and weird. While they allow us to create named objects with similarly purposed methods and properties, they're often misunderstood because of nuanced in the language itself.

But did you know that prior to 2015, JavaScript didn't even have a class keyword as part of the language?

Despite this, many programs at the time used classic Object Oriented Programming (OOP) methodologies such as using a class, extending it, and even adding static methods.

But without a class method, how did they even make classes?

A good question! Let's answer that and, along the way, look at:

• How to create a "class" without the class keyword
• How to "extend" a "class"
• How to add static methods to our "class"

Create public fields with the contructor

Let's look at a modern JavaScript class:

class User {
    name = "Corbin",
    username = "crutchcorn",
    sayCatchphrase() {
        console.log("It depends");
    }
}

This is a fairly basic class that has two properties (name and username) as well as a sayCatchphrase method.

However, despite the class keyword being added in 2015 with ES6, public fields like this weren't added until ECMAScript 2020:

So then how did classes get properties in years after 2015 but before 2020?

The answer? The constructor method:

class User {
    constructor() {
        this.name = "Corbin",
        this.username = "crutchcorn",
    }
    
    sayCatchphrase() {
        console.log("It depends");
    }
}

In fact, using this constructor method, we can even add the method as well:

class User {
    constructor() {
        this.name = "Corbin",
        this.username = "crutchcorn",
        this.sayCatchphrase = function() {
            console.log("It depends");
        }
    }
}

An interesting fact, for sure - but it doesn't answer the question of how to make a class.

Don't worry, we're getting there!

Create a class without the class keyword

Before we answer the question of "how to make a class in JavaScript without the class keyword", let's take a step back and look at what a class is actually doing...

After all, a class like User above might create an object like so:

const userObject = {
    name: "Corbin",
    username: "crutchcorn",
    sayCatchphrase: function() {
        console.log("It depends");
    }
}

Knowing this, we might think that the best way to make a class without the keyword is to return an object from a function:

function User() {
    return {
        name: "Corbin",
        username: "crutchcorn",
        sayCatchphrase: function() {
            console.log("It depends");
        }
    }
}

And sure enough, if we run this code using:

const user = new User();
user.sayCatchphrase(); // "It depends"

It will run as-expected. However, it won't solve all cases. EG:

new User() instanceof User; // false

Instead, what if we just converted the aforementioned class' constructor body to a function?:

function User() {
    this.name = "Corbin";
    this.username = "crutchcorn";
    this.sayCatchphrase = function() {
   		console.log("It depends");
	}
}

Now, not only do we have the method working, but instanceof works as well:

const user = new User();
user.sayCatchphrase(); // "It depends"
new User() instanceof User; // true

Prototype Manipulation

But surely changing from a class to a function doesn't allow you to change the prototype in the same way?

Actually, it does! That's how this whole thing works!

Consider the following code:

function User() {
    this.name = "Corbin";
    this.username = "crutchcorn";
}

User.prototype.sayCatchphrase = function() {
   console.log("It depends");
}

This is the same way of adding a method as the this.sayCatchphrase method as before, but is done by changing the prototype.

We can test this code still works by running:

const user = new User();
user.sayCatchphrase(); // "It depends"

Class Extension

function Person() {
}

Person.prototype.test = "1"


function Pix() {
}

Pix.prototype = Object.create(Person.prototype)
Pix.prototype.other = "2"

(new Pix()).test // 1
(new Pix()).other // 2

(new Person()).test // 1
(new Person()).other // undefined

Static Methods

class User {
    name = "Corbin",
    username = "crutchcorn",
    static sayCatchphrase() {
        console.log("It depends");
    }
}

function User() {
    this.name = "Corbin",
    this.username = "crutchcorn",
}

User.sayCatchphrase() {
    console.log("It depends");
}