If you want a super class to call a function from a subclass, the cleanest way is to define an abstract pattern, in this manner you explicitly know the method exists somewhere and must be overridden by a subclass.
This is as an example, normally you do not call a sub method within the constructor as the sub instance is not initialized yet… (reason why you have an "undefined" in your question's example)
abstract class A {
// The abstract method the subclass will have to call
protected abstract doStuff():void;
constructor(){
alert("Super class A constructed, calling now 'doStuff'")
this.doStuff();
}
}
class B extends A{
// Define here the abstract method
protected doStuff()
{
alert("Submethod called");
}
}
var b = new B();
Test it Here
And if like @Max you really want to avoid implementing the abstract method everywhere, just get rid of it. I don't recommend this approach because you might forget you are overriding the method.
abstract class A {
constructor() {
alert("Super class A constructed, calling now 'doStuff'")
this.doStuff();
}
// The fallback method the subclass will call if not overridden
protected doStuff(): void {
alert("Default doStuff");
};
}
class B extends A {
// Override doStuff()
protected doStuff() {
alert("Submethod called");
}
}
class C extends A {
// No doStuff() overriding, fallback on A.doStuff()
}
var b = new B();
var c = new C();
Try it Here