Using Typescript to define classes without a constructor function

Question

Using Typescript to define classes without a constructor function

As I was going through the "Tour of Heroes" guide on the Angular website, I came across the following code snippet:

class Hero {
  id: number,
  name: string,
}

const aHero: Hero = {
  id: 1,
  name: 'Superman'
}

console.log(aHero instanceof Hero); //false

I couldn't help but wonder about the purpose of this. When I examine the type of "aHero", it appears to be just a regular object and not of type "Hero". Shouldn't we simply initialize objects using a constructor as below?:

class Hero {
  constructor(id: number, name: string) {}
}

javascript angular class typescript constructor

Answer 1

Answer №1

When it comes to using class as a type, the distinction between whether something is an interface or a class becomes irrelevant. In the example provided, whether Hero is defined as an interface or a class, it serves as a type for the variable.

class Hero { id: number; name: string }

Alternatively, it can be declared as:

interface Hero { id: number; name: string }

The crucial point is that whether Hero is a class or an interface doesn't impact its usage as a type:

let hero: Hero = { id: 1, name: 'me' }

The key difference between an interface and a class lies in the fact that an interface is merely for development purposes and doesn't get converted into JavaScript. On the other hand, a class does get transpiled, and you are unable to create a new instance of an interface.

Whether there is a constructor present or not, if you use new to create an object instance, it will be considered an instanceof that class. This can be demonstrated by:

let hero = new Hero();

Executing a log of instanceof will return true because you have successfully instantiated an object of the Hero class using the keyword new.

Answer 2

When it comes to using class as a type, the distinction between whether something is an interface or a class becomes irrelevant. In the example provided, whether Hero is defined as an interface or a class, it serves as a type for the variable.

class Hero { id: number; name: string }

Alternatively, it can be declared as:

interface Hero { id: number; name: string }

The crucial point is that whether Hero is a class or an interface doesn't impact its usage as a type:

let hero: Hero = { id: 1, name: 'me' }

The key difference between an interface and a class lies in the fact that an interface is merely for development purposes and doesn't get converted into JavaScript. On the other hand, a class does get transpiled, and you are unable to create a new instance of an interface.

Whether there is a constructor present or not, if you use new to create an object instance, it will be considered an instanceof that class. This can be demonstrated by:

let hero = new Hero();

Executing a log of instanceof will return true because you have successfully instantiated an object of the Hero class using the keyword new.

Answer 3

Answer №2

While this question may have been addressed previously, when it comes to object-oriented code, the approach has typically been as follows:

It is possible to achieve the desired outcome without utilizing a constructor:

let hero: Hero = { ID: 1, Name: 'goku'};

However, if you prefer to utilize a constructor, you can implement it within the class like so:

class Hero
{
    // Utilizing optional parameters provides greater flexibility.
    constructor(id?: number, name?: string)
    {  
      this.ID = id;
      this.Name = name;
    }

    ID: number;
    Name: string
}

Furthermore, you can then instantiate the object using the following approach:

let hero: Hero = new Hero(1,'goku');
let hero2: Hero = { ID: 2, Name: 'superman' }

Answer 4

While this question may have been addressed previously, when it comes to object-oriented code, the approach has typically been as follows:

It is possible to achieve the desired outcome without utilizing a constructor:

let hero: Hero = { ID: 1, Name: 'goku'};

However, if you prefer to utilize a constructor, you can implement it within the class like so:

class Hero
{
    // Utilizing optional parameters provides greater flexibility.
    constructor(id?: number, name?: string)
    {  
      this.ID = id;
      this.Name = name;
    }

    ID: number;
    Name: string
}

Furthermore, you can then instantiate the object using the following approach:

let hero: Hero = new Hero(1,'goku');
let hero2: Hero = { ID: 2, Name: 'superman' }

Using Typescript to define classes without a constructor function

Answer №1

Answer №2

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