How to use this parameter inside a javascript object that calling a function?

Question

I am trying to call a function calcAge() inside a javascript object. calcAge() function required a parameter birthYr. If i use calcAge(1998) this is working. But i want this birthYr parameter will be the own element of that object, But this is Showing Undefined. How can i do this? and also i can i get person object retiredIn element with the returned value of that function? why person object always showing retiredIn element as a Function? i want to get it as a function output. How to do this?

I Try,

function calcAge(birthYr) {
  return 2020 - birthYr;
}
var person = {
  birthYear: 1998,
  age: calcAge(this.birthYear), //This is Showing Undefined
  retiredIn: function () {
    return 65 - this.age; //So this returns a NaN
  },
  name: "Monir",
  job: "Teacher"
};
console.log(person.birthYear); //This is Ok when i am trying to call it from outside!

console.log(person);

this.birthYear is not instanciated, when you are initialising the person object. (add console.log(bYr) to your calcAge — developer, Apr 27 '20 at 11:58
youre creating an object var person = { .. so the this variable doesnt yet exist, until after the creation has completed, so cal age cannot use it until after object has initialised — developer, Apr 27 '20 at 12:03
Use Arrow function `()=>{}` instead of regular function, your issue will be solved — ABGR, Apr 27 '20 at 12:17

score 1 · Answer 1 · answered Apr 27 '20 at 12:04

You can use a getter function instead.

function calcAge(birthYr) {
  return 2020 - birthYr;
}
var person = {
  birthYear: 1998,
  get age() {
    return calcAge(this.birthYear)
  },
  retiredIn: function() {
    return 65 - this.age;
  },
  name: "Monir",
  job: "Teacher"
};
console.log(person.birthYear); //This is Ok when i am trying to call it from outside!

console.log(person);

score 1 · Accepted Answer · answered Apr 27 '20 at 12:07

this inside the definition for person does not refer to person.

You haven't finished defining the object yet.

so you can write

function calcAge(birthYr) {
  return 2020 - birthYr;
}
var person = {};
person.birthYear= 1998;
person.age = calcAge(person.birthYear);
person.retiredIn = function () {
  return 65 - person.age; 
};
person.name = "Monir";
person.job = "Teacher";

How to use this parameter inside a javascript object that calling a function?

2 Answers2