Is there a more concise method for accepting a collection of interfaces in TypeScript?

Question

Is there a more concise method for accepting a collection of interfaces in TypeScript?

Issue

I am facing a simplified version of a problem with my model:

Here is how my model currently looks:

interface Instrument {
    name: string;
    // ...more properties shared by all instruments...
}

interface Guitar extends Instrument {
    type: "classical" | "electric";
    // ...additional properties specific to guitars...
}

interface Flute extends Instrument {
    range: "concert" | "piccolo" | "g-alto" | "g-bass";
    // ...properties unique to flutes...
}

interface Artist {
    instrument: Guitar | Flute;
}

Whenever I introduce a new instrument, I have to remember to update the list of accepted instruments for artists. I am exploring if there's a way to create an abstract instrument interface and have Artist.instrument accept all interfaces that extend Instrument.

Desired Solution

I envision a scenario like this:

interface Artist {
    instrument: // anything that extends the Instrument interface
}

I'm open to alternative solutions as well. Please suggest if there's a simpler way to tackle this issue.

Attempts Made So Far

I initially tried assigning Instrument as the type for Artist.instrument, but it didn't work as expected.

interface Artist {
    instrument: Instrument
}

interface Guitar extends Instrument {
  type: "classical" | "electric";
}

const guitar: Guitar = {
    name: "Guitar",
    type: "electric"
}

const jimiHendrix: Artist = {
    instrument: {
        name: "Guitar",
        type: "electric"
    }
}

However, this approach resulted in the following error:

TS2322: Type '{ name: string; type: string; }' is not assignable to type 'Instrument'.   Object literal may only specify known properties, and 'type' does not exist in type 'Instrument'.

javascript typescript types model

Answer 1

Answer №1

It seems like the issue arose from the code you attempted, resulting in errors that resembled the following:

interface Instrument {
    key: string;
}

interface Guitar extends Instrument {
    isElectric?: boolean;
    stringCount: number;
}

interface Flute extends Instrument {
    bodyType: "wood" | "metal";
}

interface Artist {
    instrument: Instrument
}

const artist:Artist = {
    instrument: {
        key: "A",
        stringCount: 12,
    },
};

The error specifically pointed out the stringCount property:

Type '{ key: string; stringCount: number; }' is not assignable to type 'Instrument'.
  Object literal may only specify known properties, and 'stringCount' does not exist in type 'Instrument'.

The root of the problem lies in the extensive possibilities for the properties defined by interfaces that inherit from Instrument, leaving TypeScript unable to validate unidentified properties.

To address this issue, one solution is to segregate the instrument definition into a distinct variable for better verification:

const instrument:Guitar = {
    key: "A",
    stringCount: 12,
};
const artist:Artist = {
    instrument,
};

This modification clears the errors as TypeScript can validate the instrument variable, enabling it to match the interface when assigned to the instrument property of artist.

Alternatively, another approach is to transform Artist into a generic type to explicitly specify the type of instrument the artist plays (with Instrument as the default for simplicity):

interface Artist<T extends Instrument=Instrument> {
    instrument: T
}

const artist:Artist<Guitar> = {
    instrument: {
        key: "A",
        stringCount: 12,
    }
};

Answer 2

It seems like the issue arose from the code you attempted, resulting in errors that resembled the following:

interface Instrument {
    key: string;
}

interface Guitar extends Instrument {
    isElectric?: boolean;
    stringCount: number;
}

interface Flute extends Instrument {
    bodyType: "wood" | "metal";
}

interface Artist {
    instrument: Instrument
}

const artist:Artist = {
    instrument: {
        key: "A",
        stringCount: 12,
    },
};

The error specifically pointed out the stringCount property:

Type '{ key: string; stringCount: number; }' is not assignable to type 'Instrument'.
  Object literal may only specify known properties, and 'stringCount' does not exist in type 'Instrument'.

The root of the problem lies in the extensive possibilities for the properties defined by interfaces that inherit from Instrument, leaving TypeScript unable to validate unidentified properties.

To address this issue, one solution is to segregate the instrument definition into a distinct variable for better verification:

const instrument:Guitar = {
    key: "A",
    stringCount: 12,
};
const artist:Artist = {
    instrument,
};

This modification clears the errors as TypeScript can validate the instrument variable, enabling it to match the interface when assigned to the instrument property of artist.

Alternatively, another approach is to transform Artist into a generic type to explicitly specify the type of instrument the artist plays (with Instrument as the default for simplicity):

interface Artist<T extends Instrument=Instrument> {
    instrument: T
}

const artist:Artist<Guitar> = {
    instrument: {
        key: "A",
        stringCount: 12,
    }
};

Answer 3

Answer №2

After some exploration, I managed to find a clever solution to the problem at hand.

Upon reviewing my initial question, it became clear that defining the instrument within the artist object was ineffective. It turned out that moving the definition outside and passing the variable to the artist object worked like a charm.

interface Instrument {
  name: string;
}

interface Guitar extends Instrument {
  type: "classical" | "electric";
}

interface Artist {
  instrument: Instrument;
}

const guitar: Guitar = {
  name: "Guitar",
  type: "electric",
};

const jimiHendrix: Artist = {
  instrument: guitar,
};

While this workaround resolved the issue for me, the reason that TypeScript rejects defining valid instrument properties within Artist.instrument still eludes me.

Answer 4

After some exploration, I managed to find a clever solution to the problem at hand.

Upon reviewing my initial question, it became clear that defining the instrument within the artist object was ineffective. It turned out that moving the definition outside and passing the variable to the artist object worked like a charm.

interface Instrument {
  name: string;
}

interface Guitar extends Instrument {
  type: "classical" | "electric";
}

interface Artist {
  instrument: Instrument;
}

const guitar: Guitar = {
  name: "Guitar",
  type: "electric",
};

const jimiHendrix: Artist = {
  instrument: guitar,
};

While this workaround resolved the issue for me, the reason that TypeScript rejects defining valid instrument properties within Artist.instrument still eludes me.

Is there a more concise method for accepting a collection of interfaces in TypeScript?

Issue

Desired Solution

Attempts Made So Far

Answer №1

Answer №2

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