for javascript's array why [1] ==[1] return false?

Question

In javascript,for the Array, why does:

console.log([1] == [1])

return false?

Is there any auto type-change in it? And [1] === [1] return false too?

@Thilo - Yeah, I was going to say that's at least *related*. You'd have to read fairly closely to get the *why* part from that... But there has to be a dupetarget with *why*... — T.J. Crowder, May 16 '18 at 12:58
Also: https://stackoverflow.com/questions/34102957/in-javascript-and-both-returns-false?noredirect=1&lq=1 — Thilo, May 16 '18 at 13:01

score 2 · Accepted Answer · answered May 16 '18 at 12:56

2

Because two separate objects are never == (or ===) to one another, even if they are equivalent (have the same properties with the same values). Arrays are objects.

To compare arrays, see this question's answers.

answered May 16 '18 at 12:56

T.J. Crowder

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Orelsanpls · Answer 2 · 2018-05-16T13:04:51.490

Because you are comparing two Array objects.

If you want to compare the values of the arrays you can do :

console.log([1] == [1]);

console.log(compareTwoArray([1], [1]));

console.log(compareTwoArray([1], [2]));

function compareTwoArray(arr1, arr2) {
  return arr1.length === arr2.length && arr1.every(x => arr2.includes(x));
}

Picture that you have a car, and your neighbour have the exact same car model.

If you want to strictly compare the cars, can you just look at the model? No, you will have to look at every part of the car (engine, wheels...) in order to say that they are "the same".

They are not one entity, this is two separated car, but to you, theirs characteristics make them identical.

So [1] is an array, and [1] and other array. But you would say they are identical if you look at theirs values.

But why? the `object ` be convert to hash when compare? – sinbar May 16 '18 at 12:58 — sinbar, May 16 '18 at 12:58

score 0 · Answer 3 · answered May 16 '18 at 12:58

In Javascript, Arrays are objects

typeof [1] // object

Which means when you write [1] you're creating a new object. Since the objects aren't the same object, you can't test their equality with == or ===.

See https://gomakethings.com/checking-if-two-arrays-are-equal/ for some ways to check array equality.

score 0 · Answer 4 · answered May 16 '18 at 12:58

Comparing two objects even if they are identical to each other will return false regardless of whether you use == or ===

For comparing two objects use JSON.stringify(object)

conole.log(JSON.stringify([1])==JSON.stringify([1]))

This will return true

If you want multiple comparisons you can set JSON.stringify to a variable :

let i = JSON.stringify

then you like this :

let i = JSON.stringify 
conole.log(i([1]) == i([1]))
conole.log(i([1]) === i([1]))

score 0 · Answer 5 · answered May 16 '18 at 12:59

0

Objects (Array are object) are not the same, you actually compare their addresses from the memory and since they are different instances, they are not equal.

btw, regarding primitives, you compare the actual values (not the address)

answered May 16 '18 at 12:59

omri_saadon

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for javascript's array why [1] ==[1] return false?

5 Answers5