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?
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...
}
}
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 {