Angular 5 prevent adding props to class - class

Question

I have this class
export class Alpha {
propAlpha?:string;
constructor(){
}
setProp(key: string, value: string) {
this[key] = value;
}
}
Some rest call gives me an object (response) like this:
{
propAlpha: "foo",
_someUnwanted: "bar"
}
I need to push only valid props of this object into Alpha, so I did
let myAlpha = new Alpha();
_.each(Object.keys(response), key => {
validProp(response[key]) && myAlpha.setProp(key, response[key]);
/**
* validProp() checks if value matches some criteria.
* So even if "propAlpha" is in "Alpha" it may be
* excluded for some other reason!
*/
});
the problem is that _someUnwanted is added to my class.
How can I prevent that?
I'd need to check which keys are in Alpha..
maybe like this?
if(key in myAlpha) {
myAlpha.setProp(key, response[key]);
}

Answer 1

Different approach that doesn't require declaring separate enum is to declare class members inside it's constructor. Then your Alpha class would look like this:
export class Alpha {
constructor(public propAlpha?: string){}
setProp(key: string, value: string) {
if (key in this) this[key] = value;
}
}
assigning properties wouldn't change
_.each(Object.keys(response), key => {
validProp(response[key]) && myAlpha.setProp(key, response[key]);
});

Answer 2

Really awful but I solved by doing this:
export enum AlphaPublicKeys {
propAlpha
}
let myAlpha = new Alpha();
_.each(Object.keys(response), key => {
if(key in AlphaPublicKeys){
validProp(response[key]) && myAlpha.setProp(key, response[key]);
}
/**
* validProp() checks if value matches some criteria.
* So even if "propAlpha" is in "Alpha" it may be
* excluded for some other reason!
*/
});
Hope this helps!