Lesson 9 - Classes & Objects

JavaScript Classes and Objects

Classes and Objects in JavaScript:

class Hero {
  constructor(name, health) {
    // this lets each object store its own data
    this.name = name;
    this.health = health;
  }

  toString() {
    return `Hero ${this.name} with ${this.health} health`;
  }

  say(words) {
    console.log(this.name, "says:", words);
  }
}

// Create two heroes (objects)
const h1 = new Hero("Alex", 100);
const h2 = new Hero("Maya", 80);

console.log(h1.toString());
console.log(h2.toString());
h1.say("Let's fight!");

- A class is a blueprint for creating objects.
- An object is an instance (copy) created from the class with the new keyword.
- this refers to the object itself. It lets each object keep its own data.

The constructor method

- This is a special method that runs automatically when you create a new object with new.
- It is often used to set up initial values (like a name, score, or health).

The toString() method

- A special method that describes the object as text.
- It should return a string that describes the object in a nice way.
- Careful: console.log(h1) alone shows the raw data of the object, so we call h1.toString() to get the nice message.

👉 In this example:

⚫constructor sets up each hero's name and health when it is created.
⚫toString() makes h1.toString() give a nice message instead of something confusing.
⚫this makes sure each object has its own values for name and health.

What is a Class?

A class is like a blueprint (or plan) to create objects. For example, if you have a blueprint of a house, you can use it to build many houses. In JavaScript, a class can be used to create many objects with the same structure but different data.

Objects

An object is something created from a class. If a class is a blueprint, then an object is the actual house built from it.

Example

class Dog {
  bark() {
    console.log("Woof! 🐶");
  }
}

// Create an object from the class
const myDog = new Dog();
myDog.bark();

Explanation:

class Dog { } defines the class Dog. The code of the class goes between the curly braces.
bark() is a function inside the class. Functions in a class are also called methods.
const myDog = new Dog(); creates an object from the class using new.
myDog.bark() makes the dog object use the bark method → it prints "Woof! 🐶".