How to get object of specific type from collection of its parent?-CodePudding

abstract class A {
}

export class B extends A{
}

export class C extends A{
}
....
getFirstC(aListe:A[]): C {
//get the first c object in alist
}

How to get the first element of type C from a list of type A?

We want to loop through a list of parent type(A) and find a way to identify the concrete type of each element.

According to documentation there is an example using typeof, but it is not yet clear how to use it:

type P = ReturnType<typeof f>;
    
type P = {
    x: number;
    y: number;
}

Thank you in advance

CodePudding user response：

That's not possible to achieve.

The parent class doesn't have any info what are the child classes inherited from that parent class

That means, if you are getting aListe:A[] i.e each element of Array is an object of A class, then this object can't access the properties or functions of the child classes B or C.

However, that's not true in the opposite case. If you have something like aListe:B[], then all these objects will have access to properties of A class.

CodePudding user response：

You can use instanceof, as follows:

function getFirstC(aList: A[]): C {
  return aList.find(object => object instanceof C)
}