Angular Map object from Get to Interface - json

Question

I am getting JSON object from API.
In service I have:
getUserInfo(token: string): Observable<IUser> {
return this.http.get<any>(this.apiUrl.getUser, {headers: {'X-Auth-Token': token}}).pipe(
tap(data => console.log(data)),
catchError(this.handleError)
);
}
In component:
this.authenticationService.getUserInfo(this.token).subscribe({
next: result => {
this.user = result;
console.log(this.user);
},
error: err => console.log(err)
})
This is my interface (simplified):
export class IUser {
username: string;
email: string;
role: string;
numberOfUsers: number;
expirationDate: string;
}
Is there a way to automatically map JSON from http request to that interface, so:
If property does not exist in JSON object from request, set it to
default value, for example numberOfUsers=0 or expirationDate = null.
If there is extra property in JSON object from request, just ignore
it.
Currently the user gets overwritten with values from JSON object from request.
Is there any automatic function of Objectable that would do this? Or I have to write that method in interface?

Answer 1

what you describe is a class, you can't have default values in an interface.
check class-transformer, it does what you want: https://github.com/typestack/class-transformer
It can convert a plain object to a class instance and respect default values and unrelated fields:
export class IUser {
username: string;
email: string;
role: string;
numberOfUsers: number = 0;
expirationDate: string = null;
}
this.user = plainToClass(IUser, result, {
excludeExtraneousValues: true, // <- ignores keys not for the class.
});