Cannot use "interface" declarations from TypeScript in JS (React Native tests)-CodePudding

I have a ReactNative app and I am trying to write a test using Jest. My test need to use classes from a native component (react-native-nfc-manager) and a class I need is declared like this

  export interface TagEvent {
    ndefMessage: NdefRecord[];
    maxSize?: number;
    type?: string;
    techTypes?: string[];
    id?: number[];
  }

and if I try to use this definition directly like

const event = new TagEvent();

I get this error

TypeError: _reactNativeNfcManager.default is not a constructor

I am coming from Java worlds so I think to myself - of course it cannot instantiate an interface, it needs a class so I write a test instance for this interface:

class TestTagEvent implements TagEvent {
    ndefMessage: NdefRecord[] = []
    maxSize?: number;
    type?: string;
    techTypes?: string[];
    id?: number[];
}

But the problem seem to be different since it does not work either:

TypeError: _TestTagEvent.TestTagEvent is not a constructor

What am I missing?

CodePudding user response：

You can't construct an object using an interface. An interface is just a set of properties that can be used to define required/available properties of variables.

To use the interface to initialize a variable, you want to do this:

const eventVar: TagEvent;

If you want to use TagEvent as a instantiable object, you need to define it as a class, not an interface. Something like this, where TagEventProps is the TagEvent interface you defined:

class TagEvent {
  constructor(props: TagEventProps) {
    this.ndefMesssage = props.nDefMessage;
    //etc...
  }
}

CodePudding user response：

After further experiments problem has been solved by adding 'export' to the class. Admittedly, the original error description is absolutely not matching the root cause.

export class TestTagEvent implements TagEvent {