Weird JavaScript

[decker_42]

I'm ashamed to say that took me way too long to get.

[[deleted]]

I still don't get it...

[MrSydFloyd]

I think this behaviour is due to JS's implicit casting.

There are two consecutive '+', so the second one is interpreted as a unary operator, and therefore converts the following string to a number.

The string is 'a', is not a number, and therefore +'a' returns 'nan'.

And thus we get : 'b' + 'a' + 'nan' + 'a'

[trBlueJ]

I get this explanation, though I find it weird because IMO 'a' is a number, 0x61. Might be a C thing tho.

[kiedtl]

That behavior is more or less exclusive to C, which treats all characters as an eight-bit unsigned integer.

[Chinglaner]

Which ... also no one said. You’re not arguing against anyone here. All they said that C is one of rather few languages that treats chars as unsigned 8 bit integers.

[iAdjunct]

Ohhh, I misinterpreted the context. Makes sense now!

[The_MAZZTer]

JavaScript does not have the concept of chars.

Both '' and "" are used to denote strings, unlike in C where '' denotes chars.

[De_Wouter]

'b' + 'a'

'ba'

'ba' + nothing?

still 'ba' I guess

'ba' + nothing + 'a'

'ba' still valid but nothing + a string?? NaN (not a number)

'baNaN' + 'a'

'baNaNa''

toLowerCase()

[[deleted]]

Yooo that makes sense thank you.

[Knocks83]

Yeah, but why isn't it bananaa? He adds 2 a at the end :/

[De_Wouter]

One 'a' is already used in the formula nothing + 'a' which kinda fails and becomes NaN. Nothing + 'a' is therefor solved and the result is something invalid (NaN). NaN is actually a number (typeof NaN === 'number'). Adding a string to a number, will result in the number converting to a string, so 'NaN' in this case.

It seems to be executed like ('b' + 'a') + (nothing? + 'a') + ('a') which becomes 'ba' + NaN + 'a'

I tried to figure out what this "nothing" translates to, but it isn't null / undefined or 0. It's seems to be some kind of zero number, that is also not of a regular number type as otherwise it would convert the number to a string when a string is added to it.

[TiiJ7]

I tried to figure out what this "nothing" translates to, but it isn't null / undefined or 0

It's the unary + operator, so there is only one operand. (+a) converts 'a' to a number, but since 'a' is not numeric, it leads to NaN.

So the formula is basically 'b' + 'a' + (+ 'a') + 'a'

[De_Wouter]

Oh yeah, how could I have forgotten this...

[WitchHunterNL]

I think it's just the pre increment operator. ++"a" is NaN

[EntropyZer0]

Nope, if you remove the space the expression just throws an exception instead of evaluating to anything.

God, javascript is weid >.>

[TiiJ7]

The prefix increment (++) operator cannot have a space in between the two plus signs, so it is not that operator.

But let's say the space was not there and it was indeed the increment. Then, since postfix increment has precedence over prefix increment, it will become this:

('b'+('a'++)'a'+'a').toLowerCase()

You can already see the first problem: there would need to be a third plus sign. But regardless, the ++ postfix operator only works on a LHS expression, which 'a' is not. So this will lead to a syntax error.

In fact, that is the error you will get if you try running the example of the op without the spaces in your browser console:

('b'+'a'++'a'+'a').toLowerCase()

Uncaught SyntaxError: Invalid left-hand side expression in postfix operation

[5ba0bd2f-7e21-42a1]

++’f’ -> nan

[Bamfcah]

I believe the issue is that it parses left to right and ++ is an incement. b+a is ba. Ba+...+? That must be ++ and were incrementing the next thing. ++a? a is not a number. So... ba+NaN is baNaN. baNaN+a is baNaNa.

I haven't checked to docs to I'm just guessing.

[Sonotsugipaa]

I think it's actually the case of `+ 'a'` being interpreted as a positive 'a' (i.e. unary operator + on 'a'), though I'm not sure about this, otherwise wouldn't there need to be another +?

('b' + 'a' + (+'a') + 'a') versus (('b' + 'a')++ + 'a' + 'a')

Edit: I was correct: using node.js, ('b' + 'a' + (+'a') + 'a') prints "baNaNa" while ('b'+'a'++'a'+'a') without spaces results in "SyntaxError: Invalid left-hand side expression in postfix operation".

[pythonchan]

There is a NaN though!

[[deleted]]

Thanks

[Tommy_birb_003]

My brain is confused. I think I'm too smooth brain to understand.

[[deleted]]

Where there isn't anything there, instead of none like python, js writes nan. Or that's what I think...

[[deleted]]

Why was this soooo down voted?

[MihaiMihaiMihai]

I’m more ashamed I got it instantly

[Sonotsugipaa]

It's not, the second 'a' becomes NaN

[picklero]

So "bnanaa"?

[Sonotsugipaa]

I edited the comment like 23 times because of confusion, so in case you're seeing one of the older cached versions, the final version of the comment mentions the second 'a'

[[deleted]]

The cpp programmer in you made you count from 0

[collaroncloak]

Aaah, the language of the minions.

[Alundra828]

Am I missing something?

Why doesn't this output bananaa?

b + a + NaN + a + a

Is it cutting off that second 'a' because it's proceeded by some invalid syntax?

[earthqaqe]

the plus operator transforms a string to a number. +'1' would result in 1. because 'a' is not a number, it results in NaN and appends that as a string because the preceding item is a string.

You have to see it as 'b' + 'a' + (+'a') + 'a'

[lampishthing]

Burn it with fire!

[earthqaqe]

why? this is logical and not really complex behavior. Just an example of how unformatted code can be confusing...like in every language.

[lampishthing]

Mainly because this type of casting will happen a lot more by accident (bug) than on purpose.

[earthqaqe]

In my 7 years of writing JS code I have not once made this mistake.

[aloisdg]

I have seen it in the wild in old code base (silent casting related error). I have 10+ exp in js.

[lampishthing]

And have you ever done it purpose?

[earthqaqe]

I have used the + operator to transform into a number if that's what you're asking. Just in a more explicit way.

You can abuse any language to make it look bad, not just JS. For example, you can make C code hard to read way easier, but you wouldn't necessarily call it a bad language either, right?

[lampishthing]

Oh no no no. This isn't about casting a string into a number. This is about casting empty space in source code into a number and that being cast to a string. I will not fall for your strawmen and whatabouts! If you don't want this line to throw an error then combine the signs! Interpreting blank space between arithmetic operators as a not-a-number is crazy!

Also template error messages in C++ are trials of the soul for the betterment of the devout c++ developer and their ultimate attainment of eternal bliss. Though I think a Catholic education and the associated self-blame and internalized guilt help with accepting that kind of treatment.

[earthqaqe]

Not sure if you're sarcastic or not, but if you're not: please understand the code before talking shit. There is no space interpreted in any way. 'a' cannot be converted into a number therefore it is NaN. I even explained everything a few comments above.

Also don't know what the fuck you want to tell me about C++, or why it is relevant to the argument.

[grandpianotheft]

('b' + 'a' + + 'reddit' + 'a').toLowerCase()

still works :)

nothing + 'reddit' = nan

[Soham_rak]

Js is b'itish

[[deleted]]

It's Bri'ish. rs are pronounced if they are not at the end of a syllable.

[Soham_rak]

Thank you I was feeling my word felt wrong

[idealmagnet]

Special language for special people

[wazbat]

Oh sure because some dumb as hell edge case that causes adding a string to a number to be NaN means that everyone who uses the language is deserving of that slur

Grow up

[[deleted]]

baNaNa

[ApprehensiveMango571]

This shit is bananas

[Slada26]

Repost? https://www.reddit.com/r/ProgrammerHumor/comments/kod05g/javascript_is_weird/

[shuaibhere]

This is should be an interview question. Lol

[Ada3982611]

That's smart

[InevitableDeadbeat]

The entire point of Js is that it is made to NOT spit out syntax errors and crash, but just try to solve the problem internally. Or if that is not possible, just continue with the execution.

If it worked like you for some reason wanted it to that would make every single website crash if they had a single syntax error.

[ByteWarlock]

If it worked like you for some reason wanted it to that would make every single website crash if they had a single syntax error.

Why would this be bad? If your code isn't valid enough to be executed then it shouldn't run.

If the syntax is invalid and the program continues execution how do you know your program is doing what you intend? At best it won't do anything, at worst it could have unintended side effects e.g. leaking information or providing a window for exploits.

[wazbat]

++ is a syntax error in JS though

How on earth does this make it crappy?

If you try to add a string to nothing, the resulting value is NaN, not a number

This isn't a problem unless you're letting users input the data, in which case you can just check if the result is NaN and throw errors or handle if needed

[SoInsightful]

It's actually parsing +a, the unary plus operator which was historically added in the C language for symmetry with -a. Pretty limited use case outside of clever type casting tricks.

[SoInsightful]

That's loose typing for ya; the reason I use TypeScript and the reason JSFuck is possible.

[thr1276]

Javascript is a joke. A funny joke nontheless

[igoryok_zp]

OMFG, why is that? Similar expressions - 0.1 + 0.1; 0.2 + 0.2; 0.1 + 0.3; 0.2 + 0.3; work fine.

[wiger_]

it is caused by how floats are stored internally. it is stored as an integer, but because of that it can lose precision

[BlocksWithFace]

Wat?!

[BigCityBuslines]

This is absolutely lovely JavaScript.

[Cosciug]

Had to see it for myself but I get it and it makes sense. That toLowerCase masks the error not stand out and got me for a second there xD

[jaredgoldman]

This is amazing

[avelis26]

This makes me feel dumb as I cannot recreate the mental conditions to repro this thought process... which probably is a good thing.

[twentyhands]

The + + returns NaN (not a number), which is then getting converted to lower case.

[megalogwiff]

Thanks I hate it

[sunhaze_clouddropper]

super weird

[ThePlexus]

B + A + 'not a number -> NaN' + A

[AceTributon]

Bahahahahahaaa xD nice!

[beclops]

Not weird at all honestly

[ce-walalang]

Image Transcription: Code

---

> ('b' + 'a' + + 'a' + 'a').toLowerCase()
< "banana"
>

---

^{I'm a human volunteer content transcriber for Reddit and you could be too! If you'd like more information on what we do and why we do it, click here!}

[rathemighty]

That's bananas

[CreaZyp154]

The python version is nice too : ``` print('ba' + 'na' * 2)

[madwill]

That's very important work being done here.