What are classes in JavaScript?

HighEasyJavascript

By FrontendAtlas Team · Updated Apr 4, 2026

Quick Answer

JavaScript classes are cleaner syntax over prototypes, but the practical questions are under-the-hood method sharing, field initialization, and when class-heavy modeling adds more ceremony than value.

Answer

The Core Idea

JavaScript classes are a cleaner way to define objects, methods, and inheritance, but they still run on top of prototypes under the hood. The useful question is not 'what is a class?' but when class syntax improves readability and when class-heavy modeling adds ceremony without solving a real problem.

JAVASCRIPT

// Defining a simple class
class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  greet() {
    console.log(`Hello, my name is ${this.name}`);
  }
}

const alice = new Person('Alice', 25);
alice.greet(); // Hello, my name is Alice

How Classes Work Internally

The class syntax is syntactic sugar over constructor functions and the prototype chain.

Each class has a special constructor() method that initializes new objects.

Methods defined inside a class are automatically added to the prototype, not the instance.

This keeps memory usage efficient since all instances share the same methods.

Feature	Description	Example
Constructor	A special method used for initializing objects when a class is instantiated.	`constructor(name) { this.name = name; }`
Instance Methods	Functions shared by all instances through the prototype.	`greet() { console.log(this.name); }`
Static Methods	Methods called directly on the class, not instances.	`static info() { console.log('This is a Person class'); }`
Getters & Setters	Allow controlled access to properties.	`get age() { return this._age; }`

Core components and features of JavaScript classes.

Inheritance with Classes

JavaScript supports class inheritance using the extends keyword. The child class inherits properties and methods from the parent class and can add its own. The super() keyword allows calling the parent’s constructor or methods.

JAVASCRIPT

class Animal {
  constructor(name) {
    this.name = name;
  }

  speak() {
    console.log(`${this.name} makes a sound.`);
  }
}

class Dog extends Animal {
  speak() {
    console.log(`${this.name} barks.`);
  }
}

const dog = new Dog('Rex');
dog.speak(); // Rex barks.

Behind the Scenes

Even though classes look new, they’re still built on top of JavaScript’s prototype chain:

Every class has a hidden [[Prototype]] link.

The class body methods are added to ClassName.prototype.

When you call a method on an instance, JavaScript looks it up through this prototype chain.

This means the following two approaches are equivalent in behavior:

function Person(name) {
  this.name = name;
}
Person.prototype.greet = function() {
  console.log('Hello, ' + this.name);
};

class Person {
  constructor(name) {
    this.name = name;
  }
  greet() {
    console.log('Hello, ' + this.name);
  }
}

Important Details

Class declarations are not hoisted like function declarations. You must define them before using them.

You can define anonymous classes or assign them to variables.

By default, class methods are non-enumerable, meaning they don’t show up in for...in loops.

Using new is mandatory when instantiating classes — calling a class as a function throws an error.

JAVASCRIPT

// Example: static method and getter
class MathHelper {
  static square(n) {
    return n * n;
  }

  get description() {
    return 'This class provides math utilities.';
  }
}

console.log(MathHelper.square(5)); // 25
const helper = new MathHelper();
console.log(helper.description); // This class provides math utilities.

Still so complicated?

Think of a class like a cookie cutter 🍪 — it defines the shape and design. Each cookie (object) made from it shares the same structure, but with its own details (property values).

Summary

Classes define blueprints for creating objects with shared behavior.

They simplify working with prototypes and inheritance.

Support constructors, instance methods, static methods, and getters/setters.

Classes improve code organization and readability, making OOP patterns easier to implement in JavaScript.

Under the hood, they’re still prototype-based — just easier to read and maintain.