CODEWITHSUNDEEP
javascriptfunctionthis
REINA
REINA

Reputation: 41

Having troubles to get return from a function within an object

I'm trying to understand the use of "this". I can't get the age from the function calculation(undefined). What am I doing wrong?

const reina= {
    firstName: 'Reina',
    birthYear: 1998,
    location:'Tokyo',
    friends:['Chihomi','Lei','Louis'],
    calcAge: function(){
     this.age= 2021 - this.birthYear;
    return this.age;
    }

}
console.log(reina.age);

output:

undefined

Upvotes: 1

Views: 40

Answers (2)

Rickard Elimää
Rickard Elimää

Reputation: 7591

For the sake of reusability, I would use a Class instead of assigning to an object. That would leave less code in the long run.

this points to the current scope you're in, whether your in a method, an object or a class.

To create a class, you need to add a constructor, that you can send in parameters to. As you can see in the code, this in the constructor means the class Person when I call calcAge().

I also added new Date().getFullYear() which should be self-explanatory.

class Person {
  constructor(firstName, birthYear, location, friends) {
    this.firstName = firstName;
    this.birthYear = birthYear;
    this.location = location;
    this.friends = friends;
    this.age = this.calcAge(birthYear);
  }
  
  calcAge(birthYear) {
    return new Date().getFullYear() - birthYear;
  }
}

const reina   = new Person('Reina', 1998, 'Tokyo', ['Chihomi', 'Lei', 'Louis']);
const rickard = new Person('Rickard', 1890, 'Stockholm', ['Beatrice', 'Gretchen', 'Hans']);

console.log(reina.firstName, reina.age);
console.log(rickard.firstName, rickard.age);

Upvotes: 0

Unmitigated
Unmitigated

Reputation: 89374

You never called the calcAge function.

const reina = {
  firstName: 'Reina',
  birthYear: 1998,
  location: 'Tokyo',
  friends: ['Chihomi', 'Lei', 'Louis'],
  calcAge: function() {
    this.age = 2021 - this.birthYear;
    return this.age;
  }

}
console.log(reina.calcAge());
console.log(reina.age);

It seems like a getter is most appropriate in this case.

const reina = {
  firstName: 'Reina',
  birthYear: 1998,
  location: 'Tokyo',
  friends: ['Chihomi', 'Lei', 'Louis'],
  get age() {
    return 2021 - this.birthYear;
  }
}
console.log(reina.age);

Upvotes: 2

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