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目录

JavaScript Class constructor

❮ JavaScript Classes Reference Next ❯

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");

Try it Yourself »

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:

Chrome Edge Firefox Safari Opera
Yes Yes Yes Yes Yes

constructor() is not supported in Internet Explorer 11 (or earlier).

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();

Try it Yourself »

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

❮ JavaScript Classes Reference Next ❯