具有私有属性的Typescript对象转换

Question

i am trying to cast an object into a specific class but i get the error that "_myPropertyPriv is Missing in type ClassA"

class ClassA{
    MyPropertyPub:number;
    private _myPropertyPriv
}
**later
var obj:ClassA = { MyPropertyPub:3 };

The reason i dont use a constructor is because in the real class i have theirs 20 ish properties and i dont want a constructor with that many properties.

Answer 1

There is a reason typescript does not allow this:

class ClassA{
    MyPropertyPub:number;
    private _myPropertyPriv;
    public method() {

    }

}
var obj:ClassA = <any>{ MyPropertyPub:3 }; //works
obj.method();; // runtime error, obj is not actually of type ClassA

Typescript provides the Partial type to define a type that contains a subset of the members of the original class :

var obj2:Partial<ClassA>= { MyPropertyPub:3 };

Also creating a constructor for the class using Partial and Object.assign is trivial and very useful:

class ClassA{
    MyPropertyPub:number;
    private _myPropertyPriv;

    constructor(cfg: Partial<ClassA>){
        Object.assign(this, cfg);
    }
    public method() {

    }
}

var obj3 = new ClassA({
    MyPropertyPub: 10
});
obj3.method();

Answer 2

There's no casting present in your question. You can use a type assertion (commonly referred to as a cast) to do this:

var obj:ClassA = { MyPropertyPub:3 } as ClassA; // OK