Why does the console print undefined when I access age property directly. I have to print calcAge function first in order to get the value.

const Osama = {
    firstName: 'osama',
    lastName: 'Shaikh',
    birthyear: 1999,
    job: 'developer',
    friends: ['michael', 'peter', 'steven'],
    haslicense: true,
    calcAge: function () {
        this.age = 2021 - this.birthyear;
        return this.age;
    },

};
console.log(Osama.age);

CodePudding user response：

That object doesn’t have an age property to begin with.

You only assign it when you run the calcAge method.

CodePudding user response：

It seems like you're looking to assign a getter for the age property.

const Osama = {
  birthyear: 1999,

  get age() {
    console.log('in getter');
    return 2021 - this.birthyear;
  },
};

console.log(Osama.age); // in getter, 22
console.log(Osama.age); // in getter, 22

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Or, to calculate the age only on first access and replace it with a static property you can use a self-overwriting getter.

const Osama = {
  birthyear: 1999,
  
  get age() {
    console.log('in getter');
    delete this.age;

    return (this.age = 2021 - this.birthyear);
  },
};

console.log(Osama.age); // in getter, 22
console.log(Osama.age); // 22

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