Encapsulation

Part of the Object Oriented Programming section of Coddy's JavaScript journey — lesson 17 of 56.

Encapsulation is a process of combining data inside a class within one unit.

This helps to put restrictions on accessing class data directly, eventually helping us to prevent any accidental modification of data.

Let's see encapsulation in action with a simple example. Create a basic object with public properties:

const user = {
  name: "John",
  email: "john@example.com"
};

Anyone can directly access and modify these properties:

user.name = "Jane"; // Easy to modify from outside
console.log(user.email); // Easy to access from outside

A more encapsulated approach uses closures to hide data:

function createUser(name, email) {
  // These variables are private (encapsulated)
  let userName = name;
  let userEmail = email;
  
  // Return an object with methods to interact with the private data
  return {
    getName: function() {
      return userName;
    },
    getEmail: function() {
      return userEmail;
    },
    setName: function(newName) {
      userName = newName;
    }
  };
}
const encapsulatedUser = createUser("John", "john@example.com");

Now, to interact with the data:

console.log(encapsulatedUser.getName()); // "John"
encapsulatedUser.setName("Jane");
console.log(encapsulatedUser.getName()); // "Jane"

// Cannot directly access the data
console.log(encapsulatedUser.userName); // undefined

Challenge

You're given code that uses encapsulation to protect user data. Your task is to add a getAge() method to access the age.

Tests will check:

getAge() method exists
It returns the correct age
The age info remains private

Expected Output:

john_doe

25

Cheat sheet

Encapsulation is a process of combining data inside a class within one unit and restricting direct access to that data, preventing accidental modification.

Without encapsulation, object properties are publicly accessible:

const user = {
  name: "John",
  email: "john@example.com"
};

user.name = "Jane"; // Can be modified directly
console.log(user.email); // Can be accessed directly

Using closures to encapsulate data:

function createUser(name, email) {
  // Private variables (encapsulated)
  let userName = name;
  let userEmail = email;
  
  // Public methods to interact with private data
  return {
    getName: function() {
      return userName;
    },
    getEmail: function() {
      return userEmail;
    },
    setName: function(newName) {
      userName = newName;
    }
  };
}

const encapsulatedUser = createUser("John", "john@example.com");
console.log(encapsulatedUser.getName()); // "John"
encapsulatedUser.setName("Jane");
console.log(encapsulatedUser.getName()); // "Jane"
console.log(encapsulatedUser.userName); // undefined (private data not accessible)

Try it yourself

import { createUser } from './createUser.js';

// Test code - don't modify
const user = createUser("john_doe", 25);
console.log(user.getUsername()); // Should output "john_doe"
console.log(user.getAge());      // Should output 25