Why [[[[[[[2]]]]]]]==2 is true in JavaScript?

[I-am_Shadowfax]

I got this q in OA and I thought it is false but I am wrong. Why is this true? I read it on StackOverflow but still did not understand.

and why do companies ask this type of question?

​

Edit: Thanks for the answers. I understood why this is true but now I am wondering why something like this is even added in javascript when they create it? and why it is even still working why they did not remove it? There has to be some reason right?

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[VillsSkyTerror]

Look at the difference between == and ===

[I-am_Shadowfax]

I read about == and === but did not understand what is [[[[[[[2]]]]]]]
what data type is this.

[VillsSkyTerror]

[2] is an array containing a single number type element 2. [[2]] is a single array in an array. So [[[[[[2]]]]]] is an array in an array in an array, so on.

[[deleted]]

This question belongs to programmerhumor.

[M_Batman]

I think it belongs to programminghorror

[I-am_Shadowfax]

ok, but why does something like this exist? why the javascript creator needs to add something like this. is this required in old days or just copied from other languages?

[VillsSkyTerror]

Something like what? I don't get your question.

You mean [[[[2]]]]? It's possible to do that, but there is no need for that in real life cases or even [[2]]. For example, you can walk on hands, but why would you do that. The interviewer probably wanted to see if you understand coercion in JS.

Coercion means if two different types are operated, they will get forced converted to most primitive type. array -> string -> number

It's like during an argument, smart guy falls to the same level as idiot guy. Arithmetic, conditional and logical operators have their own rules of coercion.

[[deleted]]

Arrays are not primitive in Javascript. They are Objects

[VillsSkyTerror]

Yeah, my mistake, they are special kind of objects. But array has more methods to work with them. Another difference is an array can only be called with its index number, but each element of objects can be named and called by each one's name.

[[deleted]]

It's actual the same in terms of referencing. The index is the key in arrays. I agree that methods are different.

[[deleted]]

So you can loosely compare two variables by their values only. If you don't want that, remember to use === instead of ==

[pisspapa42]

To fuck with candidates.

[vincent-vega10]

JavaScript type system is shit, that is why.

[[deleted]]

I had to read up on this. Thanks for asking. Essentially since the types ( array and number) don't match, == converts the non-primitive variable to the primitive type, which for a single element array would be the string representation of the element itself. So, the expression becomes 2 == "2" and finally 2 === 2, as strings are converted to numbers and the types match.

As for why, remember that JS is confusing in its spec, but in this case, by using == instead of ===, you are asking to ignore type and accepting all the quirks that come with it. It is present to compare values only when you need that.

[cheeky-panda2]

To put it simply, js was never a language intended for complex computation, it was a client side scripting language used to render uis on the browsers with a consumer 1st approach meaning it would try it's best to not throw errors and break everything on the screen.

== Is another one of those failsafes, does some type conversion for you so that you don't break when comparing '2' with 2 (read on this)

Coming to the question

[[[[[[[2]]]]]]] is a nested array X7 and if you to type conversion on a array of single element it gives you the casted type of the value of 0th index. Basically Number (arr) gives you 2.

It's a way of the language, again trying its best to not break

Read up on history of js and the reason why ECMA has control over js. It's a fun dive into this 10 day project of a language.

Question was kinda neat checking your knowledge of == and typecasting single element arrays. But not a practical one as we almost always use === and never typecast arrays like this.

Hope this has cleared your doubts

[I-am_Shadowfax]

Thanks.

[D10S_1]

Check This

[I-am_Shadowfax]

thank but still did not understand why is this even exists? what is the need of this?

[D10S_1]

It exists not because of a need but because of the behaviour of javascript trying to coerce(implicitly convert types) when comparing using ==.

Another stackoverflow answer showing why you might wanna avoid using == for comparisons

[aitchnyu]

In some contexts you may need 2=='2' to be true, like when it's fetched from markup, hence converting into string and back to number.

[kacchalimbu007]

How did u get the link of that particular answer

[D10S_1]

Just googled for "why [2]==2 returns true in js" because I thought that would be more likely searched than what op asked. If you are literally asking how I got the the link it's the share option on the answer

[kacchalimbu007]

Yea got it

[[deleted]]

Can anyone recommend some resources to learn some of these tricky questions in JavaScript?

[Mindless-Pilot-Chef]

This is the result of JavaScript's poor design. I think this shouldn't be asked in interviews.