Classes 101

A class is a special type of JavaScript object which is always created via a constructor. These classes act a lot like objects, and have an inheritance structure similar to languages such as Java/C#/Swift. Here's an example class: 

class Vendor {
  name: string;

  constructor(name: string) {
    this.name = name;
  }

  greet() {
    return "Hello, welcome to " + this.name;
  }
}
// An instance can be created via the new keyword, and you can call methods and access properties from the object. 
const shop = new Vendor("Ye Olde Shop");
console.log(shop.greet());
// You can subclass an object. Here's a food cart which has a variety as well as a name: 
class FoodTruck extends Vendor {
  cuisine: string;

  constructor(name: string, cuisine: string) {
    super(name);
    this.cuisine = cuisine;
  }

  greet() {
    return "Hi, welcome to food truck " + this.name + ". We serve " + this.cuisine + " food.";
  }
}
// Because we indicated that there needs to be two arguments to create a new FoodTruck, TypeScript will provide errors when you only use one: 
const nameOnlyTruck = new FoodTruck("Salome's Adobo");
// Correctly passing in two arguments will let you create a new instance of the FoodTruck: 
const truck = new FoodTruck("Dave's Doritos", "junk");
console.log(truck.greet());