Chapter 15

Classes

Classes are templates for creating an object. It encapsulates data with code to work on with data. For example if we want to make a family tree of birds, we can make a bird class and every bird object we make will have the methods and data from the bird class.

The keyword class is used to create a class. And a specific method called constructor is used for creating and initializing an object created with a class. An example of car class is shown below.

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("Toyota", 2021);
console.log(myCar.age()) // 1

In the class body, methods or constructors are defined and executed in strict mode. Syntax not adhering to the strict mode results in error.

Every time we create an object from a class we’re creating an instance of that class, for example the myCar variable above us with the new keyword is an instance. Instances are independant meaning it doesn’t affect any other instance. This is why classes are thought to be templates for objects. Since once you make that instance object it'll have the same methods as the original class.