Why Do Classes Need Attributes?

So far, our classes have been very simple—they only executed code inside the constructor.

In real applications, however, objects need to store data.

For example, a car might have information such as:

• Color
• Model year
• Manufacturer
• Speed

These pieces of information are called attributes (or properties).

Adding Attributes to a Class

Let’s modify our Car class so that it accepts a color and a model year.

class Car {
  constructor(color, model) {
    this.color = color;
    this.model = model;
  }
}

const car = new Car("Blue", 2020);

console.log(car.color);
console.log(car.model);

How Does the Constructor Receive Data?

Notice the constructor definition:

constructor(color, model);

The values inside the parentheses are called parameters. They represent the data that the constructor expects when a new object is created.

When creating the object, we provide those values:

const car = new Car("Blue", 2020);

In this example:

• "Blue" becomes the value of color.
• 2020 becomes the value of model.

What Does this Mean?

The keyword this is one of the most important concepts in Object-Oriented Programming.

When we write:

this.color = color;

we’re saying:

• this.color is the object’s own property.
• color is the value received by the constructor.

In other words, we’re copying the incoming value into the object itself.

The same idea applies here:

this.model = model;

What Does the Dot (.) Mean?

You’ve probably noticed that JavaScript uses the dot (.) very often.

The dot operator simply means:

Access something that belongs to another object.

For example:

console.log("Hello");

Here:

• console is an object.
• log is a method that belongs to that object.

The same applies to our own object:

car.color;

We’re accessing the color property inside the car object.

Likewise:

car.model;

accesses the model property.

Key Takeaways

• Attributes are the data stored inside an object.
• Constructors receive data through parameters.
• this stores those values inside the object.
• The dot operator (.) is used to access properties and methods that belong to an object.
• You can access any property using the syntax object.property.