Explanation on why the empty object instance behave differently using Object.create

Question

I ran the following in node.js v0.10.22. I understand this initial object creation snippet:

> var o1 = {};
> var o2 = Object.create(null)
> var o3 = Object.create(Object.prototype);
> var o4 = Object.create({})

> o1
{}
> o2
{}
> o3
{}
> o4
{}

> o1.prototype === void 0
true
> o2.prototype === void 0
true
> o3.prototype === void 0
true
> o4.prototype === void 0
true

However the following confuses me:

> o1 instanceof Object
true
> o2 instanceof Object
false
> o3 instanceof Object
true
> o4 instanceof Object
true

What is the explanation behind this behaviour ?

Keep in mind that object instances do not have a property prototype to access their prototype - only their constructor function would have such a property. In Chrome, for example, you can access the prototype of an object instance via o1.__proto__ — Dennis
– Dennis, Commented Feb 21, 2014 at 7:18
I get true for o4 instanceof Object when I run your code (node v0.10.13 as well as in Chrome browser console). — Ted Hopp
– Ted Hopp, Commented Feb 21, 2014 at 7:32
@TedHopp You are correct. I reran it & will update my question. — canadadry
– canadadry, Commented Feb 21, 2014 at 7:43

Community · Accepted Answer · 2017-05-23 11:43:22Z

2

When you write something like that:

var ob = {}; 
// its equivalent to Object.create(Object.prototype)

When you write:

Object.create(null) 
// doesn't inherit from anywhere and thus has no properties at all.

In other words. a javascript object inherits from Object by default, unless you explicitly create it specifying null as its prototype, as in Object.create(null)

Also you must read this question and answer, i think its great

edited May 23, 2017 at 11:43

CommunityBot

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answered Feb 21, 2014 at 7:19

Farkhat Mikhalko

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2 Comments

HelloWorld Over a year ago

great explanation. Another great resource IMO is objectplayground.com

Farkhat Mikhalko Over a year ago

@HelloWorld Thanks for you, objectplayground nice resource to learn))

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