TypeScript : Colon vs Equal To ( Angular Tutorial )

Question

I am learning Angular4 and going through the tutorial examples.

https://angular.io/docs/ts/latest/tutorial/toh-pt1.html

I have the below code in the tutoria

Answer 1

export class AppComponent { 
    title = 'Tour of Heroes'; // here you assign a value to var.  
      hero: Hero = {
      id: 1,
      name: 'Windstorm'
    };
  }

export class Hero {
  id: number; // <= here you are declaring a var to be a string but without value
  name: string;
}

you don't need to declare primitives if you assign there value immediately (number, string, boolean).