ECMAScript 2015, also known as ES6, introduced JavaScript Classes.
JavaScript Classes are templates for JavaScript Objects.
JavaScript Class Syntax
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
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Class</h2>
<p>How to use a JavaScript Class.</p>
<p id="demo"></p>
<script>
class Car {
constructor(name, year) {
this.name = name;
this.year = year;
}
}
const myCar = new Car("Ford", 2014);
document.getElementById("demo").innerHTML =
myCar.name + " " + myCar.year;
</script>
</body>
</html>
Result:
JavaScript Class
How to use a JavaScript Class.
Ford 2014
The example above uses the Car class to create two Car objects.
The constructor method is called automatically when a new object is created.
The Constructor Method
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
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Class Method</h2>
<p>How to define and use a Class method.</p>
<p id="demo"></p>
<script>
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.";
</script>
</body>
</html>
Result:
JavaScript Class Method
How to define and use a Class method.
My car is 8 years old.
You can send parameters to Class methods:
Example
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Class Method</h2>
<p>Pass a parameter into the "age()" method.</p>
<p id="demo"></p>
<script>
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.";
</script>
</body>
</html>
Result:
JavaScript Class Method
Pass a parameter into the “age()” method.
My car is 8 years old.
Browser Support
The following table defines the first browser version with full support for Classes in JavaScript:
| Chrome 49 | Edge 12 | Firefox 45 | Safari 9 | Opera 36 |
| Mar, 2016 | Jul, 2015 | Mar, 2016 | Oct, 2015 | Mar, 2016 |