Javascript: prototype attribute not visible on parent

Question

Create an object

>function Person(name) {
    this.name = name;
}

Add an attribute as a prototype. The new kind attribute does not appear on the object.

>Person.prototype.kind = 'person'

>Person
<function Person(name) {
    this.name = name;
}

Now create a new object using the parent as the prototype. The added attribute is visible.

var zack = new Person('Zack');

Person {name: "Zack", kind: "person"}

Why is the added kind attribute not visible on the parent Person object, even though it can convey it to children?

What is exacly your problem? it's not quite clear. What result did you expect? — Joel Harkes, Oct 21 '14 at 13:11
My question is why cannot I see the added attribute on the original parent object. — port5432, Oct 21 '14 at 13:12
I'm confused. Why/how do you expect `Person` to change? The prototype object only effects the objects *created* by the constructor function, not the function itself. Mutating the prototype object does not magically change the constructor function. Maybe this helps: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript . FYI `function Person` does not create an object (like you mean it). It creates a constuctor function which lets you create objects. — Felix Kling, Oct 21 '14 at 13:18
So the prototype object (Person + kind) is different from the constructor function? How can I see all the attributes of a prototype? (ie: like a class + superclass in other languages) — port5432, Oct 21 '14 at 13:23
`console.dir(Func.prototype)` . If you also want to see *instance properties*, you have to create an instance: `console.dir(new Func())`. The prototype object is the object shared by all instances created by the constructor function. It's their "prototype". — Felix Kling, Oct 21 '14 at 13:42

score 2 · Accepted Answer · answered Oct 21 '14 at 13:17

This is beceause Person is just a funtion(object)/Constructor:

Person =
function Person(name) {
    this.name = name;
}

To Get the kind object on person refer to the prototype

Person.prototype =
Person {kind: "person"}

Im not an expert in this but if you would want to create a new constructor you should overwrite the function.

You could see the function (below) as an constructor to set instance specific variables

    function Person(name) {
        this.name = name;
    }

Person.prototype.kind = 'person' is like a static variable on the class

score 1 · Answer 2 · answered Oct 21 '14 at 13:24

1

You are looking at the Person Constructor.

To look at the properties of the definition of a Person you can use Object.getOwnPropertyNames(Person.prototype)

This would show the kind property.

answered Oct 21 '14 at 13:24

2 Answers2