Welcome to the OOP station! Today, we're going to dive into constructors in TypeScript classes. Constructors play an essential role in creating and initializing objects. Picture a constructor as a blueprint — it details the components necessary for creating each object.

Just like JavaScript, if you don't provide a constructor in your TypeScript class, a default one will be supplied. Imagine this scenario as being given a blank blueprint sheet ready for you to customize!

In TypeScript, constructors are defined using the keyword constructor within a class. These constructors can have parameters that initialize the properties of class instances. Think of this as specifying the components needed for a blueprint and their respective quantities. Let's exemplify this:

class Car {
  brand: string;
  model: string;
  color: string;

  constructor(brand: string, model: string, color: string) {
    this.brand = brand;  
    this.model = model;  
    this.color = color;  
    console.log(`Instantiated a Car instance with brand=${brand}, model=${model}, color=${color}`);
  }
}

Note that in TypeScript, we have to declare the types of the class properties before assigning them in the constructor. Each time we create a new Car object, we need these attributes to be supplied. You'll learn more about attributes in upcoming lessons.

Let's create our first Car object using the new keyword:

let myCar = new Car("Toyota", "Corolla", "red");
// Prints a message from the constructor:
// Instantiated a Car instance with brand=Toyota, model=Corolla, color=red

myCar is a Car object, representing a red Toyota Corolla. This object has properties defined by the constructor!

Although a TypeScript class can host numerous methods, it is bound by one condition — it can only accommodate a single constructor. If we attempt to declare more than one constructor, TypeScript will raise a SyntaxError.

In instances where no explicit constructor is defined, TypeScript provides a default one: constructor() {}.

Furthermore, we can assign default values to parameters as shown below:

class Car {
  brand: string;
  model: string;
  color: string;

  // 'color' has a default value of "white"
  constructor(brand: string, model: string, color: string = "white") {
    this.brand = brand;
    this.model = model;
    this.color = color;
  }
}