JavaScript: Classes and Basic Syntax

Introduction to JavaScript Class Syntax

In JavaScript, classes provide a syntax for more traditional object-oriented programming, but they do more than just offer a new syntax. They provide a clear and concise way to construct object blueprints, which can be instantiated and manipulated at runtime. This guide focuses on explaining the basic syntax and usage of JavaScript classes, a key concept introduced in ECMAScript 2015 (ES6) that has become a fundamental part of modern JavaScript development.

Defining a Class in JavaScript

A class in JavaScript is defined using the class keyword, followed by the class name and a pair of curly braces. Here is the basic structure:

class MyClass {
  // Class body definition

Constructor Method

The constructor method is a special method for creating and initializing an object created with a class. It runs automatically when a new instance of the class is created. Continue reading for executable examples.

class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;

In this example, the Rectangle class is designed to require height and width parameters when an object is instantiated, initializing each new rectangle with these properties.

Creating an Instance of a Class

To create an instance of a class, you use the new keyword, which creates a new object and calls the constructor to initialize it:

class Rectangle { constructor(height, width) { this.height = height; this.width = width; } } const rectangle = new Rectangle(10, 20); console.log(rectangle.height);

This code snippet creates a new instance of Rectangle with a height of 10 and a width of 20.

Class Methods

Methods added to the class definition act as prototypes for the instances of the class. Here is how to add a method to our Rectangle class:

class Rectangle { constructor(height, width) { this.height = height; this.width = width; } area() { return this.height * this.width; } } const rectangle = new Rectangle(10, 20); console.log(rectangle.area());

The area method can be called on any instance of the Rectangle class.

Static Methods

Static methods are called on the class itself, not on instances of the class. They are useful for utility functions that you want to group with the class, but that do not operate directly on instance data. Static methods are called using the class name.

class Rectangle { static whoAmI() { return "I am a Rectangle class"; } } console.log(Rectangle.whoAmI()); // Outputs: "I am a Rectangle class"


JavaScript classes provide a structured approach to object-oriented programming in JavaScript. By understanding the syntax and functionality provided by classes, such as constructors, instance methods, and static methods, developers can create more maintainable and organized code. Classes enforce a cleaner, modular structure that can be easier to understand and work with, especially in large projects. As JavaScript continues to evolve, the importance of mastering classes and their syntax will only grow.

Practice Your Knowledge

What are the key features of JavaScript 'class' syntax?

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