Typescript: Implementing abstract class does not force you to implement all methods but it should?

[ORESoftware]

Potentially a bug, or just unexpected behavior. So I have this abstract class:

export abstract class Transformer {

  abstract identifyViaRawStr: () => boolean;
  abstract identifyViaJSObject: (v: any) => boolean;
  abstract getValue: (v:any) => string;
  abstract transformToBunionFormat: (v: any) => BunionJSON

}

and then I implement it with another class:

const c = new (class implements Transformer{

  getValue(v: any) {
    return '';
  }

  identifyViaJSObject: (v: any) => boolean;
  identifyViaRawStr: () => boolean;
  transformToBunionFormat: (v: any) => BunionJSON;

});

the above compiles fine, but looks funny since 3/4 methods are not implemented. It transpiles without an error to:

class Transformer {
}
exports.Transformer = Transformer;
const c = new (class {
    getValue(v) {
        return '';
    }
});

I mean maybe this is correct, but it's not expected at least for me.

[jcalz]

Is this a bug report? If so, there's a template. Is this a feature request? If so, there's a template. Is this a question? If so, this is not the place for it. I'm surprised you could create a new issue without being presented these options and associated templates. Oh well.

The code above looks like intended behavior when you have the --strictPropertyInitialization compiler option disabled. You should consider enabling it.

[fatcerberus]

You've declared your methods as properties. Since those properties are declared in the subclass, TS treats them as implemented. You just didn't initialize them, which is a separate problem. If you're still confused:

abstract class C {
    abstract foo: number;
}

class D extends C {
    foo: number;  // <-- foo is now implemented
}

Also, you should use extends for class inheritance, not implements. I don't feel like you fully understand how class works...

[ORESoftware]

You've declared your methods as properties

I don't understand, how else would you declare them?

[jcalz]

@ORESoftware I'm not a member here so I can't modify your issue, sorry. When I start creating an issue with my phone I still get the template, so... 🤷.

I'll reiterate: the compiler is working as intended here and there is no bug. Questions belong elsewhere, such as Stack Overflow. Good luck.

[ORESoftware]

@jcalz pls chill dogg, this was a potential bug - when you file a bug ticket, you don't know for sure if it's bug or not, or just unexpected behavior.

[jcalz]

❄️🐶👍

[fatcerberus]

class C {
    abstract method();
}

class D extends C {
    method() { ...implementation... }
}

If you’re not intending to implement something in the derived class, don’t declare it. If you do and it’s not declared abstract, TS considers it to be implemented.

[RyanCavanaugh]

@ORESoftware abstract classes have been in the language for years; it's a bad guess that we just completely forgot to check how they work with interfaces and that no one else noticed either. Please stop using the issue tracker as a place to resolve your own surprises. If behavior isn't clearly broken, you should assume it's not a bug.