How to properly add a new public field to a class in TypeScript?

Question

typescript

I'm trying TypeScript.

class Main {
    constructor(public name: string) {}
}

class Sub extends Main {
    constructor(name: string, public lastname: string) {
        super(name)
    }
}

const sub = new Sub('michael', 'jackson')

function hello (person: Main) {
    console.log(person.name)
    console.log(person.lastname)
}

hello(sub)

I get this error:


What am I doing wrong and how correct is the syntax?
I understand that the error is natural, that there is no such property in the Main class. But I need to pass another class inherited from Main to the function.

Don't hit the noob :(

Answer 1

In general, interfaces were invented for such things:

interface ISubMain {
    name: string;
    lastname: string;
}
class Main {
    constructor(public name: string) {}
}

class Sub extends Main implements ISubMain {
    constructor(name: string, public lastname: string) {
        super(name)
    }
}

const sub = new Sub('michael', 'jackson')

function hello (person: ISubMain) {
    console.log(person.name)
    console.log(person.lastname)
}

hello(sub)

Answer 2

Well, or just check that the class came exactly the right one.)

class Main {
    constructor(public name: string) {}
}

class Sub extends Main {
    constructor(name: string, public lastname: string) {
        super(name)
    }
}

const sub = new Sub('michael', 'jackson')

function hello (person: Main) {
    console.log(person.name)
    if(person instanceof Sub) {
        console.log(person.lastname)
    }
}

hello(sub)