Introduction to Encapsulation in JavaScript

Welcome back! We're shifting our focus to another essential concept in Object-Oriented Programming (OOP): encapsulation. Encapsulation helps us bundle the data (variables) and methods (functions) that operate on the data into a single unit called a class. It also restricts access to some of the object's components, ensuring data integrity and security.

Encapsulation is a fundamental concept in object-oriented programming that involves bundling the data (variables) and methods that operate on the data into a single unit or class. This helps protect the data from unauthorized access and modification.

In JavaScript, encapsulation can be achieved by using private class fields or closures:

1. Private Class Fields: Use the # symbol to define private fields in a class, restricting direct access from outside the class.
2. Closures: Encapsulate variables within functions, creating a private scope that is not accessible from outside.

Encapsulation enhances the modularity, maintainability, and security of your code by preventing unauthorized access and modifications to an object's internal state.

Let's look at the following JavaScript example to get a better understanding of encapsulation using private class fields:

class Person {
    #name;
    #age;

    // Constructor
    constructor(name, age) {
        this.#name = name;
        this.#age = age;
    }

    // Setters
    setName(name) {
        this.#name = name;
    }

    setAge(age) {
        if (age >= 0) {
            this.#age = age;
        } else {
            console.error('Age cannot be negative.');
        }
    }

    // Getters
    getName() {
        return this.#name;
    }

    getAge() {
        return this.#age;
    }
}

// Example usage
const person = new Person('Alice', 30);
person.setName('Bob');
person.setAge(25);

console.log(`Name: ${person.getName()}, Age: ${person.getAge()}`);

In this example, we have a Person class with private fields #name and #age. The class provides methods (setName, setAge, getName, and getAge) for manipulating and accessing these private fields.

If we skip setters and getters and make the data fields accessible, we lose control over the data and can't enforce constraints or validations. Encapsulation allows us to protect the object's internal state and provide controlled access to it. Additionally, encapsulation enables us to include logic within setter methods, such as validating that the age is not set to a negative value.