CODEWITHSUNDEEP
javascriptinheritance
Happy Coconut
Happy Coconut

Reputation: 1063

Inheritance in Java​Script

I have a class Person like this:

 class Person {
    constructor(name, age, gender, interests) {
        Object.assign(this, {name, age, gender, interests});
    }
}

And I can make sub-class like this:

class Teacher extends Person {
    constructor(name, age, gender, interests, subject, grade) {
        super(name, age, gender, interests);
        Object.assign(this, {subject, grade});
    }
}

But what if I want to make sub-class but I don't want to inherit all the properties from the Person class. For example I don't want to inherit the interests property. Do I just exclude it like this:

class Student extends Person {
    constructor(name, age, gender, height, weight) {
        super(name, age, gender); // I haven't included the interests property here
        Object.assign(this, {height, weight});
    }
}

I am still beginner so I am not sure if this is good practice or not. Have a nice day!

Upvotes: 1

Views: 515

Answers (2)

Jonas Wilms
Jonas Wilms

Reputation: 138235

  super(name, age, gender); // I haven't included the interests property here

By not adding an argument to a function call, the parameter will implicitly be undefined. The upper therefore equals:

 super(name, age, gender, undefined)

Therefore the interests property does still exist, it is just undefined. That is actually a good solution if all your code assumes that interests could not be defined. If not, e.g. if you are doing calculations with it without an explicit check, your calculations might suddenly be NaN, which gets you into some trouble:

  if(person.age > 18) {
   alert("adult");
  } else alert("child"); // or maybe the person is not a child, and it's age property was just not set?

Now instead of setting that existing property to a value that indicates that it is undefined, you could omit the interests property at all, by:

1) Moving it to a subclass:

 class Person {
   constructor(name, age, gender) {
    Object.assign(this, {name, age, gender });
  }
 }

 class PersonWithInterests extends Person  {
   constructor(name, age, gender, interests) {
    super(name, age, gender);
    Object.assign(this, { interests });
  }
}

2) Create a Mixin:

A Mixin is a class, that can extend more than one class. If more than a Person has an interest, it might be benefitial to create a mixin for it:

 const Interested = Super => class InterestMixin extends Super {
  constructor(args) { // passing in an object here makes the Mixin more flexible, all superclasses have to deal with it though
    super(args);
    this.interests = args.interests;
  }
};

class Animal { }

const PersonWithInterest = Interested(Person);
const AnimalWithInterest = Interested(Animal);

new PersonWithInterest({ name: "Jonas", interests: 10 })
new AnimalWithInterest({ type: "bear", interests: 20 })

(If you end up creating a new Mixin for every single property, this solution is not really viable anymore. If you can't group multiple properties into a useful Mixin, go with the first way instead (having optional properties)).

Upvotes: 4

HRK44
HRK44

Reputation: 2742

Inheritance means what it means ... you inherit what the parent gives to you. So 'avoiding attributes' it not really recommended (and I'm not sure you can even do it).

Two solutions :

  • Architecture wise (that I recommend): in your specific case, I would just put interests in the Teacher class. If other classes would have the interests too, I would create a sub-class like PersonInterest on which Teacher would inherit from.
  • Code wise: you set interests to null or undefined in the class where you don't need it.

Upvotes: 4

Related Questions