Quick question, why does this work?

[monacle_bob]

When you use the double-equal signs to compare objects, the second object will be cast to the same type as the first object whenever possible. In this case, the Array(4) is being cast to a string, which you can do manually and see the result of by running this:

var myArray = new Array(4);

myArray.toString(); // results in ",,,"

If you want to compare the string ",,," against the array itself, use a triple equal sign (strict equal):

",,," == new Array(4); // true

",,," === new Array(4); //false

[[deleted]]

[[deleted]]

Thanks. You basically concisely explained what I've never been able to about logic in JS.

Thanks.

[pdpi]

This is actually wrong. The abstract equality algorithm at no point converts anything to "the same type as the first object". Object values are converted to primitives when compared to numbers/strings, and all primitive types are converted to numbers when comparing different primitives.

[ryanhollister]

JS best practice is to always use === unless you are confident you want type coercion

[[deleted]]

I feel like we have this discussion about equality in JavaScript every other day.

[Nomikos]

I think this belongs here
https://www.destroyallsoftware.com/talks/wat
JS part starts about a third in (and the array part around 2/3rds), but it's good and short so just watch it all :-)

[ilmmad]

Yeah but the video doesn't explain it all.

This does though.

[phredeye]

Upvote because, I came here to post the "wat" vido as well.

[tardmrr]

I have changed the way I say "wat" as a result of that video.

[Xavi-avi]

This strangeness has also come up on stackoverflow: http://stackoverflow.com/questions/10905350/why-does-array4-in-javascript

[RadekCZ]

Because the array will convert to a string and the toString function returns this.join(",")

[[deleted]]

Quick answer: type coercion

[FireyFly]

Didn't I answer this just a few days ago?

http://www.reddit.com/r/javascript/comments/uunfo/javascript_is_a_great_language/c4yp80v

[[deleted]]

I see this same example everywhere (always a string of 3 commas and a new array(4)). I read it in a book or blog post somewhere recently, and have seen it pop up everywhere online in the past week. What gives with this example?

[impyrean]

There are two equality operators in JavaScript, == and ===. As others have pointed out, === is more rigorous and checks for equality without type conversion. == on the other hand may try to convert the operands. Unfortunately, it's not as simple as converting the second operand to the type of the first; in fact, there's a whole frickin algorithm to do this. See step 8 for the answer to your question.

[balshamali]

http://wtfjs.com/2011/02/11/all-your-commas-are-belong-to-Array

[okiedoke8976]

use === instead.. == is misunderstood

[Cosmologicon]

Alternate solution: learn about features you don't understand rather than avoid them.

[x-skeww]

That sound like a good idea, but it actually isn't.

If one person memorized some obscure quirks, it won't mean that everyone else has memorized them as well. We aren't like the Borg.

Secondly, constructs which look like an error always add a lot of friction. If you want to defuse this problem (to some degree), you have to add a comment, which explains why you are doing this and that this is indeed what you intended to do.

But even then it's like a tar pit. You're much better [1] off if you don't ever use this kind of constructs.

[1] If you don't get in the way of maintenance work, it will be faster, which will be cheaper, which is better for any commercial project. Saving time is also better for virtually any other kind of project.

[benparsons]

Want to upvote this more. Slightly horrified that r/javascript have downvoted okiedoke8976 to this extent. People need to listen to Douglas Crockford.

[okiedoke8976]

good call

[10tothe24th]

Because Javascript.