typescript initialize object with partial object literal

Question

I want to initialize an instance of a class with an object literal not containing all the elements in the class but whose elements are in the class.

class ATest{
    aStr:string;
    aNum:number;

    result(){return this.aStr + this.aNum;}
}
let test=new ATest;

test={aStr:"hello",aNum:12};   // error, result() is missing in the object literal

What is the way to do that assignment exploiting the most of the validations of ts?

test=Object.assign(test,{aStr:"hello",aNom:12});

would work but then you miss the validation of the input fields - see aNom that's wrong but gets in

Answer 1

You have an object literal, an instance of a class must be created using new ClassName()

The simplest solution is to add a constructor accepting a Partial<T>

class ATest{
    aStr:string;
    aNum:number;
    constructor(obj: Partial<ATest>) {
        Object.assign(this, obj);
    }
    result(){return this.aStr + this.aNum;}
 }

 let test=new ATest({aStr:"hello",aNum:12});

Inside this new constructor you can do validations of the fields as required.