Abstract Classes

Abstract Class

Abstract Class is a class that can't be instantiated (objects cannot be created).

It's supposed to represent something abstract and not specific.

Let's look at the following example:

class Vehicle { getInsuranceCost(months){ return 0; } constructor() { if (this.constructor === Vehicle) { throw new Error('Abstract class "Vehicle" cannot be instantiated directly.'); } } } class Car extends Vehicle { // Overwriting method getInsuranceCost(months) { return 25 * months; } } class Bicycle extends Vehicle {} // let vehicle = new Vehicle(); let car = new Car(); console.log( "Car's Year Insurance: " + car.getInsuranceCost(12) + " $"); let bicycle = new Bicycle(); console.log( "Bike's Year Insurance: " + bicycle.getInsuranceCost(12) + " $");

Output:

Car's Year Insurance: 300 $ Bike's Year Insurance: 0 $

Explanation

• The abstract class Vehicle is defined at lines 1-12.
• The name of the abstract class is Vehicle. This is something indefinite and it's inherited by other classes.
• If we uncomment line 24 the code won't compile. That's due to the error set at line 9.