Oppiskele Calling Parent Constructors with super

When you create a subclass in JavaScript using the extends keyword, the subclass inherits properties and methods from its parent class. However, to properly initialize the parent class's properties within the subclass's constructor, you must use the super keyword. The super keyword acts as a reference to the parent class's constructor and allows you to call it from within the subclass. This is essential because, in JavaScript, a subclass constructor cannot access this until after it has called super. By calling super, you ensure that all properties defined in the parent class are correctly set up before you add or modify properties specific to the subclass. This mechanism not only enables property inheritance but also allows you to extend or customize the initialization process for your subclasses.


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// Parent class
class Vehicle {
  constructor(make, model) {
    this.make = make;
    this.model = model;
  }
}

// Subclass
class Car extends Vehicle {
  constructor(make, model, doors) {
    super(make, model); // Call parent constructor
    this.doors = doors; // Additional property for Car
  }
}

const myCar = new Car("Toyota", "Corolla", 4);
console.log(myCar.make); // Output: Toyota
console.log(myCar.model); // Output: Corolla
console.log(myCar.doors); // Output: 4

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// Parent class
class Vehicle {
  constructor(make, model) {
    this.make = make;
    this.model = model;
  }
}

// Subclass
class Car extends Vehicle {
  constructor(make, model, doors) {
    super(make, model); // Call parent constructor
    this.doors = doors; // Additional property for Car
  }
}

const myCar = new Car("Toyota", "Corolla", 4);
console.log(myCar.make); // Output: Toyota
console.log(myCar.model); // Output: Corolla
console.log(myCar.doors); // Output: 4

Oliko kaikki selvää?

Kiitos palautteestasi!

Osio 2. Luku 2