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8.1 JS Classes
- ECMAScript 2015, also known as ES6, introduced JavaScript Classes.
- JavaScript Classes are templates for JavaScript Objects.
JavaScript Class Syntax
- Use the keyword to create a class.
- Always add a method named :
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 1: JS Classes
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 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 to create a class.
- Always add a 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 2: JS Class Methods
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 3: JS Class Methods part 2
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.";
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 |
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