Why Object() != Object() in JavaScript?

Question

So the question is that two same objects are not equal in JavaScript, let's say:

Object() == Object()

or even:

[{a: 1}, {a: 2}].indexOf({a: 1}); //returns -1 not found

What's the reason of this strange behavior?

Those are two similar objects, they certainly are not the same. — Musa, Sep 01 '14 at 19:13
Maybe that helps: http://stackoverflow.com/questions/201183/how-to-determine-equality-for-two-javascript-objects/16788517 — John, Sep 01 '14 at 19:16
@AfshinMehrabani There isn't a predefined way to determine the *similarity* or "*deep equality*" of 2 objects -- e.g., they both only have 1 property, `a`, with the same value, `1`. Though, some libraries, such as Underscore, do define functions for this purpose. — Jonathan Lonowski, Sep 01 '14 at 19:18
@WillemD'haeseleer came from Python, that seems a strange behavior to me. — Afshin Mehrabani, Sep 01 '14 at 19:23
According to https://osrc.dfm.io/afshinm/ you are in the top 10% most active JavaScript users on github, but you come here with a question like this. I find that really confusing. But props for learning I guess.. — Willem D'Haeseleer, Sep 01 '14 at 19:40
@WillemD'haeseleer the reason for this strange question is this strange tweet https://twitter.com/afshinmeh/status/506500753251651584 ;-) — Kamran Ahmed, Sep 01 '14 at 19:47

score 8 · Accepted Answer · answered Sep 01 '14 at 19:13

8

Objects are compared by reference. And two references are equal only if they point to the same object.

answered Sep 01 '14 at 19:13

jonasnas

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Is that a correct behavior? Do we have the same behavior in other languages such as Python? – Afshin Mehrabani Sep 01 '14 at 19:19
2

@AfshinMehrabani yep. in Python ``The "is" operator tests object identity. Python tests whether the two are really the same object (i.e., live at the same address in memory).`` – doniyor Sep 01 '14 at 19:23
To prevent confusion: In JS You might stumble on `Object.is`, which will also test for identity on objects, only strict, and not broken like `===`... – Willem D'Haeseleer Sep 01 '14 at 19:33

score 2 · Answer 2 · edited May 23 '17 at 12:29

Objects are reference and when you compare two reference they return false.

The other answer(given by Eamon Nerbonne) here has a very relevant point:

Objects are considered equivalent when

They are exactly equal per === (String and Number are unwrapped first to ensure 42 is equivalent to Number(42))

or they are both dates and have the same valueOf()

or they are both of the same type and not null and...

they are not objects and are equal per == (catches numbers/strings/booleans)

or, ignoring properties with undefined value they have the same properties all of which are considered recursively equivalent.

score 1 · Answer 3 · answered Sep 01 '14 at 19:23

1

Same applies for Arrays ([] === []) //returns false

And NaN is a special value as well which is never equal to itself.

NaN === NaN //False

answered Sep 01 '14 at 19:23

Kiba

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Why Object() != Object() in JavaScript?

3 Answers3