How to get properties of Javascript object prototype?

Question

I'd like to get _firstName and _birthDate from : I tried https://jsfiddle.net/0xLqhufd/

var Person = (function () {
function Person(firstName, birthDate) {
    this._firstName = firstName;
    this._birthDate = birthDate;
}
return Person;
}());

alert(Object.keys(Person.Prototype));

You aren't currently using the prototype as far as I'm aware. To see the properties of an object you would have to look at the keys of an instance. The protype normally only contains methods or static variables. — HopefullyHelpful
– HopefullyHelpful, Commented Apr 4, 2016 at 11:27
_firstName and _birthDate aren't properties of Person.prototype (and it's prototype, lower case, not Prototype). — T.J. Crowder
– T.J. Crowder, Commented Apr 4, 2016 at 11:28

Rajaprabhu Aravindasamy · Accepted Answer · 2016-04-04 11:32:08Z

3

You cannot get an object's properties before creating a new instance.

Object.keys(new Person)

Also for your understanding, you have properties with your current instance not in prototype. At this moment your prototype will be empty and it inherits the Object's, The core one, that holds toString etc. And those are non enumerable, so you cannot get those by using Object.keys().

DEMO

edited Apr 4, 2016 at 11:32

answered Apr 4, 2016 at 11:27

Rajaprabhu Aravindasamy

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2 Comments

T.J. Crowder Over a year ago

"At this moment your prototype will be the core one" No, it won't. It'll be an object with no properties of its own other than constructor, which inherits toString and such from its prototype.

Rajaprabhu Aravindasamy Over a year ago

@T.J.Crowder Yes the Object's prototype. I meant to say that. Let me correct my words there

Tushar · Accepted Answer · 2016-04-04 11:27:27Z

2

This is factory function. You need to create instances of the class using new.

var Person = (function () {
    function Person(firstName, birthDate) {
        this._firstName = firstName;
        this._birthDate = birthDate;
    }
    return Person;
}());

var tushar = new Person('Tushar', '15464');
console.log(tushar); // { _firstName: 'Tushar', _birthDate: '15464' }

answered Apr 4, 2016 at 11:27

Tushar

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Comments

Chrillewoodz · Accepted Answer · 2016-04-04 11:27:31Z

1

You need to create a new person:

var newPerson = new Person('Lars', 'Svensson');

console.log(newPerson.firstname);
console.log(newPerson.birthDate);

This will allow you to access it's properties.

answered Apr 4, 2016 at 11:27

Chrillewoodz

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