JavaScript equality from Underscore docs

Question

I saw this on the underscore.js docs under _.isEqual. Why is this the case?

var moe   = {name: 'moe', luckyNumbers: [13, 27, 34]};
var clone = {name: 'moe', luckyNumbers: [13, 27, 34]};
moe == clone;
=> false

Is it because strings and numbers aren't objects so they can be compared, but JS doesn't allow you to compare Arrays or Object Literals which are Objects?

Identity comparison. They're referencing two different objects. — user2736012
– user2736012, Commented Oct 13, 2013 at 5:05

Community · Accepted Answer · 2017-05-23 12:21:08Z

3

Object literal always defines a new object and thus variables moe and clone refer to different objects.

An expression comparing Objects is only true if the operands reference the same Object

Comments

Joke_Sense10 · Accepted Answer · 2013-10-13 05:18:58Z

0

Use JSON.stringify property:

JSON.stringify(moe) === JSON.stringify(clone)

Note: Order of the properties is very important. In this case, properties of moe should be in the same order as properties of clone or vice-versa.

answered Oct 13, 2013 at 5:18

Joke_Sense10

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2 Comments

Dan Hlavenka Over a year ago

That will work assuming it's an exact copy, but will fail if the keys are out of order, such as clone = {luckyNumbers: [13, 27, 34], name: 'moe'}. The objects are still effectively the same (order doesn't technically matter), but would fail the JSON test. The only true way to test equality is to recursively iterate over the entire object.

Joke_Sense10 Over a year ago

I agree with you. Thus the only way would be to compare the properties of variables recursively.

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