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JavaScript

Posted by Kristian Woods
Kristian Woods
23,414 Points

Why am I returning the value 'NAN'?

I understand that NAN means 'not a number'. But I can't understand why I'm returning that value. 

class Person {
    constructor(name) {
        this._name = name;
        this._age = 28;
    }

     static addYear(year) {
         return this._age += year;
    }

     get age() {
        return this._age;
    }

}

Person.addYear(1);

console.log(Person.age);

Thanks

1 Answer

Steven Parker
Steven Parker
243,318 Points
Steven Parker
Steven Parker
243,318 Points

The Person class itself has no "_age" member (but an instance of it would). So when the call is made to addYear, it creates a new variable. But it is unable to establish a value using the addition assignment operator because it had none to begin with. The result of adding 1 to an undefied is "NaN".

Also, I would expect the addYear method to be more useful if it was not a static method, since it would then have access to the instance variable using "this".