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JavaScript Introducing ES2015 Classes Sub-Classes

Nick Field
Nick Field
17,091 Points
Posted by Nick Field
Nick Field
17,091 Points

Calling the super function...

In this video example, the super function is used to call methods on the parent class

class Student extends Person {
  constructor({name, age, interestLevel = 5} = {}) {
     super({name, age});
     this.name = name;
     this.age = age;
     this.interestLevel = interestLevel;
  }
}

let stevenJ = new Student ({name: 'Steven', age: 22, interestLevel: 1});

However, defining this.name = name and this.age = age in the sub-class is not needed, since those methods are already defined in the parent function already, so the following is valid-

class Student extends Person {
  constructor({name, age, interestLevel = 5} = {}) {
     super({name, age});
     this.interestLevel = interestLevel;
  }
}

Which case is better practice here? The second case is more DRY, are there any negative effects of using this approach?

M Ashraful Alam
M Ashraful Alam
12,328 Points

Exactly what I was going to ask, then I saw your question.

4 Answers

Steven Parker
Steven Parker
229,786 Points
Steven Parker
Steven Parker
229,786 Points

Your second example is a best-practice subclass. :+1: Good job!

I notice in the video the subclass is made by copying the parent class and then editing it, I assume these two lines were just overlooked.

Lean Rasmussen
Lean Rasmussen
11,060 Points
Lean Rasmussen
Lean Rasmussen
11,060 Points

I feel like the super({}) Is hardly explained am I the only one ?

Jens Filipsson
Jens Filipsson
12,870 Points
Jens Filipsson
Jens Filipsson
12,870 Points

Thanks Nick, your very question was what made me understand the super concept. With this.name = name and this.age = age defined in the sub class, the super function didn't make sense to me. So once again, a big thank you!

Peter Retvari
seal-mask
.a{fill-rule:evenodd;}techdegree
Peter Retvari
Full Stack JavaScript Techdegree Student 8,392 Points
Peter Retvari
.a{fill-rule:evenodd;}techdegree
Peter Retvari
Full Stack JavaScript Techdegree Student 8,392 Points

Million thanks for this question. I didn't understand either that WHY WE HAVE TO DEFINE THE NAME AND AGE if we inherit from the person class. And it could be 'super' frustrating when you just started to learn this concept.