📘 JavaScript Objects and Classes

Presented by Swapnil Meshram within mentorship Devsync

🎓 Started learning JavaScript with the guidance of Devsync, focusing on concepts of objects and classes with simple hands-on practice.

✅ What are Objects in JavaScript?

In JavaScript, an object is a collection of key-value pairs. It’s used to group related data and functionality together.

An object can contain:

• Properties (data)

• Methods (functions)

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📌 1. Creating an Object

🔹 Using Object Literal

let person = {
  name: "Alice",
  age: 25,
  city: "Mumbai",
  greet: function () {
    console.log("Hello, my name is " + this.name);
  }
};

🔍 Explanation:

• name, age, and city are properties.

• greet is a method.

• this.name ⁣refers to the current object’s name ⁣property.

🔹 Accessing Object Properties

console.log(person.name);     // Output: Alice
console.log(person["city"]); // Output: Mumbai

🔹 Calling a Method

person.greet(); // Output: Hello, my name is Alice

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📌 2. Adding & Modifying Object Properties

person.country = "India";       // Add new property
person.age = 26;                // Modify property

🔹 Deleting a Property

delete person.city;

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📌 3. Nested Objects

let student = {
  name: "Rahul",
  marks: {
    math: 90,
    science: 85
  }
};

console.log(student.marks.math); // Output: 90

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📌 4. for...in Loop to Iterate an Object

for (let key in person) {
  console.log(key + ": " + person[key]);
}

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✅ What are classes in JavaScript?

A class is a blueprint for creating objects with predefined properties and methods. It was introduced in ES6 (ECMAScript 2015).

Classes make your code more organised and reusable, especially when creating multiple similar objects.

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📌 5. Declaring a Class

class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  greet() {
    console.log("Hi, I’m " + this.name);
  }
}

🔍 Explanation:

• constructor() is a special method that initialises object properties.

• this.name and this.age refer to the properties of the object created.

• greet() is a method inside the class.

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📌 6. Creating Objects from a Class

let user1 = new Person("Amit", 30);
let user2 = new Person("Priya", 28);

user1.greet(); // Output: Hi, I’m Amit
user2.greet(); // Output: Hi, I’m Priya

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📌 7. Adding Methods Outside Constructor

You can define multiple methods in a class:

class Car {
  constructor(brand) {
    this.brand = brand;
  }

  start() {
    console.log(this.brand + " is starting...");
  }

  stop() {
    console.log(this.brand + " is stopping...");
  }
}

let myCar = new Car("Toyota");
myCar.start(); // Output: Toyota is starting...

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📌 8. Inheritance with Classes

A class can inherit properties and methods from another class using extends.

class Animal {
  constructor(name) {
    this.name = name;
  }

  speak() {
    console.log(this.name + " makes a sound.");
  }
}

class Dog extends Animal {
  speak() {
    console.log(this.name + " barks.");
  }
}

let dog = new Dog("Tommy");
dog.speak(); // Output: Tommy barks.

🔍 Explanation:

• Dog inherits from Animal using extends.

• The speak()method is overridden in the Dogclass.

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📌 9. Getters and Setters in Classes

🔹 Getters

Used to access object properties like methods.

class Circle {
  constructor(radius) {
    this._radius = radius;
  }

  get area() {
    return Math.PI * this._radius ** 2;
  }
}

let c = new Circle(5);
console.log(c.area); // Output: 78.54 (approx)

🔹 Setters

Used to change private-like properties.

class Circle {
  set radius(r) {
    this._radius = r;
  }

  get radius() {
    return this._radius;
  }
}

let c = new Circle();
c.radius = 10;
console.log(c.radius); // Output: 10

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📌 10. Static Methods

A static method belongs to the class itself, not any instance.

class MathUtils {
  static square(x) {
    return x * x;
  }
}

console.log(MathUtils.square(5)); // Output: 25

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✅ Summary: Objects vs Classes

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🧠 Final Tips

• Use objects when you just need to group related data.

• Use classes when creating multiple similar objects or for OOP (Object-Orientated Programming).

• Practice by creating classes for products, students, vehicles, or employees.