I've no idea why this prints NaN. HEEELP!

Question

function person(name, age, color) {
this.name = name;
this.age = age;
this.skincolor = color;
this.YearOfBirth = Born();
}

function Born() {
return 2019 - this.age;
}

var p1 = new person("Jane ", 42, "white");

document.write(p1.YearOfBirth);

Answer 1

Try

function person(name, age, color) {
this.name = name;
this.age = age;
this.skincolor = color;

this.born = function() {
return 2019 - this.age;
}
this.YearOfBirth = this.born();
}

var p1 = new person("Jane ", 42, "white");

document.write(p1.YearOfBirth);

Answer 2

Mystic Life Atleast it does not look like Java at all.
Java would look like this:

class Person {
private String name;
private int age;
private String skincolor;
private int YearOfBirth;

Person(String name, int age, String color) {
this.name = name;
this.age = age;
this.skincolor = color;
this.YearOfBirth = this.Born();
}

private int Born() {
return 2019 - this.age;
}
}

class MyClass {
public static void main(String args[]) {
Person p1 = new Person("Jane ", 42, "white");

System.out.println(p1.YearOfBirth);
}
}

Answer 3

Mystic Life this represents an object self.
You can give this object variables:
this.age = 400;

The variables won't be confused with other object variables.
You can have 2 or more objects with the same object variable name.
Objects can also have functions.

Answer 4

How would function Born know what is "this"?

Shortly the problem is in that you used this-keyword in Born-function.

But I assume you can make a solution or 2 by yourself.

Answer 5

Mystic Life Could you explain why it does not look like JavaScript?

Answer 6

Seb TheS I understood your point. Thanks.

Answer 7

Did you copy it from java? It doesn't seem like javascript. Because person function is like a java class constructor.

Answer 8

What is the purpose using "this" in the person function?