TypeScript class with null properties when initializing

Question

I have started a new Next.js project with typescript with npx create-next-app --example with-typescript with-typescript-app (https://github.com/zeit/next.js/tree/master/examples/with-typescript).

How ever when I try to create a class like this:

export class Programm {
    id: string;
    name: string;
    thumbnailUrl: string;
}

I get the syntax error:

Property 'id' has no initializer and is not definitely assigned in the constructor.ts(2564)

when I add a constructor like this:

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

It works. Why is that and how can I create an object so the properties are null when initializing the class?

The same code is working without the constructor in angular

Answer 1

You can define your properties as optional, with a ? modifier:

export class Programm {
     id?: string;
     name?: string;
     thumbnailUrl?: string;
}

Now if you initialize a new instance of type "Programm", properties will have undefined value.