JavaScript Classes are templates for JavaScript Objects. Use the keyword class to create a class. Always add a method named constructor():
Syntax
class ClassName {
constructor() { … }
}Example
class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
}
The example above creates a class named “Car”. The class has two initial properties: “name” and “year“.
A JavaScript class is not an object. It is a template for JavaScript objects.
Using a Class
When you have a class, you can use the class to create objects:
Example
let myCar1
= new Car("Ford", 2014);
let myCar2
= new Car("Audi", 2019);
The example above uses the Car class to create two Car objects.
The Constructor Method
The constructor method is called automatically when a new object is created. The constructor method is a special method:
- It has to have the exact name “constructor”
- It is executed automatically when a new object is created
- It is used to initialize object properties.
If you do not define a constructor method, JavaScript will add an empty constructor method.
Class Methods
Class methods are created with the same syntax as object methods. Use the keyword class to create a
class. Always add a constructor() method. Then add any number of methods.
Syntax
class ClassName {
constructor() { ... }
method_1() { ... }
method_2() { ... }
method_3() { ... }
}Create a Class method named “age”, that returns the Car age:
Example
class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
age() {
let date = new Date();
return date.getFullYear() -
this.year;
}
}
let myCar
= new Car("Ford", 2014);
document.getElementById("demo").
innerHTML =
"My car is " + myCar.age() + "
years old.";
You can send parameters to Class methods:
Example
class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
age(x) {
return x - this.year;
}
}
let date = new Date();
let year = date.getFullYear();
let myCar
= new Car("Ford", 2014);
document.getElementById("demo").
innerHTML=
"My car is " + myCar.age(year)
+ " years old."
