Declaring a class type variable in Typescript

Question

I'm having trouble understanding line 18 of the following snippet of a TypeScript tutorial.

1   class Greeter {
2       static standardGreeting = "Hello, there";
3       greeting: string;
4       greet() {
5           if (this.greeting) {
6               return "Hello, " + this.greeting;
7           }
8           else {
9               return Greeter.standardGreeting;
10          }
11      }
12  }
13  
14  let greeter1: Greeter;
15  greeter1 = new Greeter();
16  console.log(greeter1.greet());
17  
18  let greeterMaker: typeof Greeter = Greeter;
19  greeterMaker.standardGreeting = "Hey there!";
20  
21  let greeter2: Greeter = new greeterMaker();
22  console.log(greeter2.greet());

As I understand from the tutorial, the goal of the declaration of greatermaker is getting the Greeter class type into a variable, rather than the instance type.

Firstly, what is the function of the assignment operator = in this line?

Secondly, what do we mean exactly with the distinction between the class type and the instance type? I guess, in the first we are able to manipulate the static member variables as opposed to the second?

Edit.

Why don't we just use let greeterMaker: typeof Greeter, that is without the assignment operator?

Answer 1

(Tentative) expansion of @JGoodgive's comment.

An important thing to note is the distinction bewteen:

• the TypeScript type reference Greeter, as in let var : Greeter;
• the JavaScript instance type of class Greeter, as in var = new Greeter; typeof var;
• the JavaScript class type variable, which embodies the class constructor itself, as in var = Greeter.

It is key to note that the class type variable var = Greeter is in fact the class constructor function. Hence, it is, incidentally and in particluar, of type Greeter; because that is the class of which it is a public member function.

On another note, typeof Greeter should return Greeter according to the tutorial. This is because by Greeter in typeof Greeter, we mean the constructor function of the class Greeter. And since, the constructor function returns the class itself (as an instance), it [the constructor function Greeter] is of class type Greeter, indeed.

Answer 2

The goal is to have the reference copy of the Greeter class (actually function) into the variable greeterMaker. With these you have 2 variables greeterMaker and Greeter to refer to the same class. So you can create objects of that class via

new Greeter()

or

new greeterMaker()

These two statements will do the same thing, because greeterMaker is just another variable which refers to the Greeter.