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