I am trying to print out the name of class B or C in it's super class (A). Is there a way to infer this somehow from the context? Do I have to pass in the names into super as a parameter or is there a better way of doing this?

class A {
  constructor() {
    // klass_name is some code to get the name of class B,C
    console.log(klass_name)
  }
}

class B extends A {
}

class C extends A {
}

I am trying to print out the name of class B or C in it's super class (A). Is there a way to infer this somehow from the context? Do I have to pass in the names into super as a parameter or is there a better way of doing this?

class A {
  constructor() {
    // klass_name is some code to get the name of class B,C
    console.log(klass_name)
  }
}

class B extends A {
}

class C extends A {
}

• javascript

3 Answers 3

Yes, there are two ways you can access it where you've shown:

• this.constructor.name (assuming nothing has messed around with it), which you can use anywhere that has access to the instance
• new.target.name (only available in the constructor; new.target has the value undefined in function calls that aren't part of a new operation)

But other than logging purposes and such, it's rare for the superclass to need to know anything about the subclass.

Example:

class A {
  constructor(){
    console.log("this.constructor.name = " + this.constructor.name);
    console.log("new.target.name = " + new.target.name);
  }
}

class B extends A {
}

class C extends A {
}

new C;

The constructor property is automatically set up on a class's prototype to refer to the class's constructor, and as of ES2015 functions (including constructors) have a name property on them giving their name. Since the instance inherits from the prototype, you can use constructor on it to access that constructor and its name.

The new.target meta-property is available in functions to provide a reference to the constructor function that was used in the new expression.

Side note: When your subclass constructor is nothing but a call to the superclass constructor, you can leave it off entirely. The JavaScript engine will add one for you.

An instance can get a hold of its constructor function via this.constructor. The name of the function is available as the property .name. So, it's surprisingly straight forward:

console.log(this.constructor.name)

this.constructor.name

Should do the trick.