Introduction

In Object-Oriented Programming (OOP), an instance is an individual object created from a class. A class acts as a blueprint, while an instance is the actual object that contains its own data and can use the methods defined in the class.

For example, if Employee is a class, you can create multiple employee objects such as John, Alice, and David. Each of these objects is called an instance of the Employee class.

In Node.js, instances are created using the new keyword. Every instance has its own copy of the object’s properties while sharing the methods defined in the class.

For automation engineers, creating instances is essential when working with the Page Object Model (POM). Each page class is instantiated so that its methods can be used to automate browser interactions.

In this tutorial, you’ll learn how to create and use instances in Node.js.

What is an Instance?

An instance is an object created from a class.

A class is a blueprint.
An instance is the actual object created from that blueprint.

Example:

class Employee {

}

const employee =
    new Employee();

Here:

Employee is the class.
employee is an instance of the class.

Why Create Instances?

Instances allow developers to:

Create multiple objects from one class.
Store different data in each object.
Reuse the same methods.
Organize application data.
Build scalable applications.
Follow object-oriented programming principles.

Example 1: Create an Instance

class Student {

}

const student =
    new Student();

console.log(student);

Sample Output

Student {}

Example 2: Create Multiple Instances

class Employee {

}

const employee1 =
    new Employee();

const employee2 =
    new Employee();

console.log(employee1);

console.log(employee2);

Sample Output

Employee {}
Employee {}

Although both objects are created from the same class, they are different instances.

Example 3: Instance with Properties

class Employee {

    name = "John";

    department = "IT";

}

const employee =
    new Employee();

console.log(employee.name);

console.log(employee.department);

Sample Output

John
IT

Example 4: Instance with Methods

class Employee {

    greet() {

        console.log(
            "Welcome Employee"
        );

    }

}

const employee =
    new Employee();

employee.greet();

Sample Output

Welcome Employee

Example 5: Multiple Independent Instances

Each instance maintains its own state.

class Counter {

    count = 0;

}

const counter1 =
    new Counter();

const counter2 =
    new Counter();

counter1.count = 5;

counter2.count = 10;

console.log(counter1.count);

console.log(counter2.count);

Sample Output

5
10

Example 6: Check an Instance

Use the instanceof operator to determine whether an object is an instance of a class.

class Employee {

}

const employee =
    new Employee();

console.log(
    employee instanceof Employee
);

Sample Output

true

Real-World Example

Create multiple product objects.

class Product {

    name = "Laptop";

    price = 75000;

}

const product1 =
    new Product();

const product2 =
    new Product();

console.log(product1.name);

console.log(product2.price);

Sample Output

Laptop
75000

Automation Testing Example

Instances are widely used in automation frameworks.

Playwright Example

Create an instance of a page object.

class LoginPage {

    login() {

        console.log(
            "Login Successful"
        );

    }

}

const loginPage =
    new LoginPage();

loginPage.login();

Selenium Example

Create an instance of a search page.

class SearchPage {

    search() {

        console.log(
            "Searching Product"
        );

    }

}

const searchPage =
    new SearchPage();

searchPage.search();

Cypress Example

Create an instance of a dashboard page.

class DashboardPage {

    open() {

        console.log(
            "Dashboard Opened"
        );

    }

}

const dashboard =
    new DashboardPage();

dashboard.open();

API Testing Example

Create an instance of an API client.

class ApiClient {

    sendRequest() {

        console.log(
            "API Request Sent"
        );

    }

}

const api =
    new ApiClient();

api.sendRequest();

Data-Driven Testing Example

Create multiple employee instances.

class Employee {

    name = "Employee";

}

const emp1 =
    new Employee();

const emp2 =
    new Employee();

console.log(emp1.name);

console.log(emp2.name);

Common Mistakes

Forgetting the `new` Keyword

Incorrect:

const employee =
    Employee();

Correct:

const employee =
    new Employee();

Without new, JavaScript throws an error for class constructors.

Assuming Two Instances Are the Same Object

class Employee {

}

const emp1 =
    new Employee();

const emp2 =
    new Employee();

console.log(emp1 === emp2);

Sample Output

false

Each call to new creates a separate object.

Calling Methods Without Creating an Instance

Incorrect:

Employee.greet();

Correct:

const employee =
    new Employee();

employee.greet();

Best Practices

Always use the new keyword when creating class instances.
Use meaningful variable names for instances.
Create multiple instances when representing different objects.
Keep class definitions reusable.
Avoid creating unnecessary instances.
Use instances to access class properties and methods.
Organize instances logically within your application.

Conclusion

Creating instances is one of the most important concepts in Object-Oriented Programming. A class defines the blueprint, while an instance is the actual object created from that blueprint.

For automation engineers, creating instances is a daily practice when working with the Page Object Model (POM), API clients, utility classes, and reusable components.

Understanding how to create and use instances is essential before learning constructors, inheritance, encapsulation, polymorphism, and other advanced OOP concepts.

Frequently Asked Questions (FAQs)