JavaScript Class constructor
Example
Create a Car class, and then create an object called "mycar" based on the Car class:
class Car {
constructor(brand) { // Constructor
this.carname = brand;
}
}
mycar = new Car("Ford");
More "Try it Yourself" examples below.
Description
The constructor() method is a special method for creating and initializing objects created within a class.
The constructor() method is called automatically when a class is initiated, and it has to have the exact name "constructor", in fact, if you do not have a constructor method, JavaScript will add an invisible and empty constructor method.
Note: A class cannot have more than one constructor() method. This will throw a SyntaxError.
You can use the super() method to call the constructor of a parent class (see "More Examples" below).
Browser Support
constructor() is an ECMAScript6 (ES6) feature.
ES6 (JavaScript 2015) is supported in all modern browsers since June 2017:
| Chrome 51 | Edge 15 | Firefox 54 | Safari 10 | Opera 38 |
| May 2016 | Apr 2017 | Jun 2017 | Sep 2016 | Jun 2016 |
constructor() is not supported in Internet Explorer.
Syntax
constructor(parameters)
Technical Details
| JavaScript Version: | ECMAScript 2015 (ES6) |
|---|
More Examples
To create a class inheritance, use the extends
keyword.
A class created with a class inheritance inherits all the methods from another class:
Example
Create a class named "Model" which will inherit the methods from the "Car" class:
class Car {
constructor(brand) {
this.carname =
brand;
}
present() {
return 'I have a ' + this.carname;
}
}
class Model extends Car {
constructor(brand, mod) {
super(brand);
this.model = mod;
}
show() {
return this.present() + ', it is a ' + this.model;
}
}
mycar = new Model("Ford", "Mustang");
document.getElementById("demo").innerHTML
= mycar.show();
The super() method refers to the parent
class.
By calling the super() method in the
constructor method, we call the parent's constructor method and get access to
the parent's properties and methods.
Related Pages
JavaScript Tutorial: JavaScript Classes
JavaScript Tutorial: JavaScript ES6 (EcmaScript 2015)
JavaScript Reference: The extends Keyword
JavaScript Reference: The super Keyword