Javascript Classes

JavaScript classes, introduced in ECMAScript 2015, are syntactical sugar over JavaScript's existing prototype-based inheritance, providing a clearer and more concise way to create objects and deal with inheritance. They serve as templates for creating new objects, encapsulating both properties and methods. Understanding the use and implementation of classes is crucial for efficient object-oriented programming in JavaScript.

Javascript Classes Javascript Classes

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Table of contents

    Understanding Javascript Classes

    Javascript classes are a core part of modern programming in Javascript, enabling you to create objects with shared behaviour and characteristics. This guide will walk you through what Javascript classes are, their syntax, and how to use their properties effectively. An essential read for anyone looking to deepen their understanding of Javascript and object-oriented programming.

    What are Javascript Classes?

    Javascript Classes are templates for creating objects. They encapsulate data for the object and methods to manipulate that data, all within a single, tidy package.

    In essence, a class is a blueprint for objects. Just as an architect's plans are used to build houses that share the same design, a Javascript class is used to create objects that share the same properties and methods. This concept is fundamental to understanding object-oriented programming, making code more reusable, and systems easier to maintain.

    Think of a class as a recipe, and objects created from the class as dishes made using that recipe.

    JavaScript Class Syntax Fundamentals

    Understanding the basic syntax of Javascript classes is crucial to utilising their power in programming projects. The syntax for creating a class involves the class keyword, followed by the class name and braces that encapsulate the class body.

    class Car {
      constructor(brand) {
        this.brand = brand;
      display() {
        console.log('The brand of the car is ' + this.brand);

    In the example above, Car is a class with a constructor method and a display method. The constructor method is a special function that creates and initializes an object instance of the class. The this keyword refers to the current instance of the class.

    Every class in Javascript automatically has a constructor method, even if you don't define one. If not defined, a default constructor is used.

    Javascript Class Properties: A Primer

    Properties are variables that belong to a class. They represent the attributes or characteristics of the objects created from the class. Understanding how to define and use properties is central to leveraging the full potential of Javascript classes.

    Class Properties are variables that are accessible within class methods and represent the state of an object.

    class Person {
      constructor(name, age) { = name;
        this.age = age;
      describe() {
        return + ' is ' + this.age + ' years old.';

    In the Person class example above, name and age are properties of the class. They are defined within the constructor and can be used within any method of the class, like the describe method, which uses these properties to return a string describing the person.

    Advanced concepts in Javascript classes, such as static properties and methods, inheritance, and getter/setter methods, further extend the capabilities of classes. Static properties are shared among all instances of a class and can be accessed without creating an instance. Inheritance allows a class to inherit properties and methods from another class. Getters and setters enable more controlled access to class properties.

    Properties defined directly within the class body, without the this keyword, are considered static properties.

    Diving Into Javascript Class Constructors

    Understanding the pivotal role of constructors within Javascript classes paves the way for mastering object-oriented programming in Javascript. This section delves into class constructors, highlighting their importance, defining their syntax, and showcasing their practical use through examples.

    The Role of the Javascript Class Constructor

    The constructor in a Javascript class serves as the blueprint for initializing new objects. When you create a new instance of a class, the constructor function is automatically called, setting up the object with its initial properties and behaviors. The constructor makes it straightforward to create multiple objects with the same properties but different values.

    You can think of the constructor as the 'birth' of an object, where it gets its initial characteristics.

    How to Define a Javascript Class Constructor

    Defining a constructor within a Javascript class is accomplished by using the constructor method. This special method is syntactically similar to functions, but it’s exclusively used within class definitions. The constructor can take parameters, allowing you to pass values to the object when it is instantiated.

    Here’s the basic syntax for a class constructor:

    class Vehicle {
      constructor(make, model) {
        this.make = make;
        this.model = model;

    In this example, Vehicle is a class with a constructor that takes two parameters: make and model. These parameters are used to initialise the class’s properties when an instance of the class is created.

    Simplifying a Javascript Class Example with Constructors

    Let's simplify the concept of constructors with a practical example. Suppose we want to model a simple Book class, which contains properties for title, author, and year of publication. By utilising a constructor, we can easily create multiple instances of books with different characteristics.

    class Book {
      constructor(title, author, year) {
        this.title = title; = author;
        this.year = year;
      getSummary() {
        return `${this.title} was written by ${} in ${this.year}.`;

    This Book class includes a constructor and a getSummary method. The constructor is used to initialise the book's properties upon creation, while getSummary is a method defined to output a brief description of the book.

    By comprehending how to define and use constructors, you can streamline object creation and enhance readability and maintainability of your code. Constructors not only initialise object properties but also pave the way for implementing more sophisticated programming concepts, such as inheritance and polymorphism, within class-based structures.

    It's also worth noting that constructors play a crucial role in dynamic object creation patterns, offering flexibility in how objects are created and initialised throughout a Javascript application.

    Exploring Inheritance with Javascript Classes

    Delving into inheritance within Javascript classes unveils a powerful paradigm for reusing and managing code effectively. This exploration introduces the principles of inheritance, how to implement it using the extends keyword, and practical examples to consolidate understanding.

    What Does Javascript Class Inheritance Mean?

    Javascript Class Inheritance is a mechanism wherein a class (called a child or subclass) inherits properties and methods of another class (known as a parent or superclass).

    Inheritance is a fundamental concept in object-oriented programming that promotes code reusability and hierarchy. In Javascript, it allows developers to create a class hierarchy, where subclasses can inherit from superclasses, reducing redundancy and fostering a more organised and scalable codebase.

    Inheritance mirrors real-world relationships. Just as a child inherits characteristics from their parents, a subclass inherits from a superclass in Javascript.

    Mastering Javascript Class Extends Keyword

    The extends keyword in Javascript plays a pivotal role in facilitating class inheritance. It enables a subclass to inherit properties and methods from a superclass, forming a hierarchical relationship between classes.

    Usage of the extends keyword ensures that the subclass not only acquires the superclass’s properties and methods but can also have its unique attributes or override inherited methods.

    class Animal {
      constructor(name) { = name;
      speak() {
        console.log(`${} makes a noise.`);
    class Dog extends Animal {
      speak() {
        console.log(`${} barks.`);

    In this example, Dog is a subclass of Animal. By using the extends keyword, Dog inherits properties and methods from Animal, but also defines its method speak to override the one from Animal.

    The super keyword can be used within a subclass to call the constructor and methods of the superclass.

    Crafting a Javascript Class Example with Inheritance

    Crafting examples with inheritance in Javascript offers a practical insight into how classes can be structured to make code more reusable and scalable. Let’s consider an example where we extend a base class to create more specific subclasses.

    class Shape {
      constructor(name) { = name;
      display() {
        console.log(`This is a ${}.`);
    class Circle extends Shape {
      constructor(radius) {
        this.radius = radius;
      area() {
        return Math.PI * this.radius * this.radius;

    Here, Circle is a subclass of Shape. It uses the extends keyword to inherit from Shape, and super to call the constructor of Shape, assigning 'circle' as the name. Besides inherited properties and methods, Circle also introduces an area method specific to circles.

    Implementing inheritance in Javascript enhances code modularity and reusability. By creating a hierarchy of classes where subclasses extend superclasses, developers can build a well-organised, scalable codebase. This approach reduces redundancy and promotes a clearer understanding of the relationships and responsibilities among different classes. Embracing the power of inheritance and the extends keyword allows for writing more maintainable and efficient code in larger projects.

    Implementing Methods in Javascript Classes

    Implementing methods in Javascript classes unlocks a world of possibilities for adding functionality to class instances. Methods are functions associated with a class that enable instances of the class to perform actions or operations. This section will guide you through defining and utilising methods within classes, their significance in programming, and provide a practical example for a clearer understanding.

    Defining and Utilising Javascript Class Methods

    Defining methods within a Javascript class is similar to defining a regular function, but with the context provided by the class itself. Methods can perform operations using the class’s properties and can be called on any instance of the class. They are defined inside the class block, using a concise syntax without the function keyword.

    class Calculator {
      constructor(value) {
        this.value = value;
      add(number) {
        this.value += number;
        return this;
      subtract(number) {
        this.value -= number;
        return this;

    In the Calculator class above, the add and subtract methods allow the manipulation of the class’s value property. Notice the methods allow chaining by returning the instance (this).

    Methods can return this to enable method chaining, where multiple methods can be called on the same instance sequentially.

    The Significance of Javascript Class Methods in Programming

    Javascript class methods play a crucial role in programming, enabling objects to not just hold data but to actually do something with that data. Methods enhance encapsulation, one of the core concepts in object-oriented programming, by keeping the actions an object can perform closely bundled with the object itself.

    Furthermore, methods promote code reuse and maintainability. By defining a method once in a class, any instance of that class can utilise the method without the need to duplicate code.

    Practical Javascript Class Example Utilising Methods

    A practical example will solidify understanding of how methods enhance classes in Javascript. Consider a class Rectangle, which will include methods to calculate the rectangle’s area and perimeter.

    class Rectangle {
      constructor(length, width) {
        this.length = length;
        this.width = width;
      area() {
        return this.length * this.width;
      perimeter() {
        return 2 * (this.length + this.width);
    const myRectangle = new Rectangle(10, 5);
    console.log(myRectangle.area());  // Outputs: 50
    console.log(myRectangle.perimeter());  // Outputs: 30

    The Rectangle class defines two methods: area and perimeter. These methods operate on the class properties length and width to calculate and return the rectangle’s area and perimeter. An instance of the Rectangle class can easily utilise these methods to get the area and perimeter, showcasing the power of incorporating methods into classes.

    Understanding and leveraging methods within Javascript classes is a foundational skill for any aspiring programmer. Through examples and explanations, it’s evident how methods contribute to code organisation, encapsulation, and reusability. As one progresses in their programming journey, exploring more advanced method types, such as static methods, getters, and setters, further expands the horizons of what can be achieved with classes and objects in Javascript.

    Javascript Classes - Key takeaways

    • Javascript Classes are templates for creating objects with encapsulated data and methods to manipulate that data.
    • The class constructor is a special method for creating and initialising an object instance of a class, using the this keyword to refer to the instance.
    • Javascript class inheritance allows a class to inherit properties and methods from another class using the extends keyword.
    • Class properties represent the state of an object and are defined within the constructor, while class methods are functions that belong to the class and can perform operations on its properties.
    • Advanced concepts like static properties and methods, inheritance, and getter/setter methods extend the capabilities of Javascript classes, promoting code reusability and maintainability.
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    Frequently Asked Questions about Javascript Classes
    What is the syntax for creating a class in JavaScript?
    The syntax for creating a class in JavaScript involves the `class` keyword followed by the class name. Inside curly braces, you can define a constructor method for initialising objects and other class methods. For example: `class MyClass { constructor() { ... } method1() { ... } }`.
    How can you inherit properties from another class in JavaScript?
    In JavaScript, you can inherit properties from another class by using the `extends` keyword. When defining your class, you follow its name with `extends` and then the name of the class you want to inherit from. This mechanism enables you to adopt methods and properties from the parent class.
    What are static methods in JavaScript classes and how do you use them?
    Static methods in JavaScript classes are functions that belong to the class itself, rather than any instance of the class. You use them by referencing the class name, followed by the method name, e.g., `ClassName.methodName()`. They are useful for utility functions that don't rely on object instance properties.
    How can you create private properties and methods within a JavaScript class?
    In JavaScript classes, you can create private properties and methods by prefixing them with a hash (#) symbol. These elements are then only accessible within the class itself, making them truly private. For example, `#myPrivateMethod()` or `#myPrivateProperty`.
    What is the purpose of the constructor method in a JavaScript class?
    The constructor method in a JavaScript class is used to initialise new objects of the class. It runs automatically when a new instance is created, allowing the setup of properties or the execution of any start-up procedures the object might need.

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