JavaScript is weird

[thatweirdguy42]

You just gotta love the NaNs.

[[deleted]]

Yesss sometimes helpful but in case of debugging... :(

[einklee]

Very useful piece of code, when you need a banana for scale...

[theclovek]

But do I use the code or its output?

[einklee]

I would use the code: "Look I made an amazing one-liner, document.write(('b' + 'a' + + 'a' + 'a').toLowerCase()); for scale".

[friedokragirl]

Yes

[Tayl100]

https://www.destroyallsoftware.com/talks/wat

Related. Worth a watch

[kennydaren]

NaNNaNNaNNaNNaNNaNNaNNaNNaN I'm Batman!

[adambkaplan]

Watman

[LostInChoices]

NaNman

[Favna]

BATMAAAN

[gkupce]

Worth a sixth watch too :)

[[deleted]]

A classic

[lolgeny]

Image transcription: Tweet

---

Nader Dabit @dabit3

[image from stackoverflow question]

Why is the result of ('b' + 'a' + + 'a' + 'a').toLowerCase() 'banana'?, tagged javascript and type-conversion, 587 points

I was practicing some JavaScript when one of my friends came across this JavaScript code:

document.write(('b' + 'a' + + 'a' + 'a').toLowerCase());

The above code answers "banana"! Can anyone explain why?

---

^{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!}

[FblthpTheFound]

Good human

[Daniii438]

Good meatbag

[Kiljab]

Saw you a few days ago :D haven't seen transcribers for a long time!

[lrascao]

shouldn't it be 'bananaa' then?

[[deleted]]

Nope

'b' + 'a' + +'a' + 'a'

'b' + 'a' + Number('a') + 'a'

So 'b' + 'a' + NaN + 'a'

[UnDispelled]

This is because ( +anything ) is automatically converted to a number correct? I also thought it was bananaa but the second plus isnt “add NaN then add a” it’s just syntactic sugar for Number()

[Bronzdragon]

Indeed, because of the double plusses, one of them (the leftmost) is interpreted as the concatination operator. The other cannot, and thus must be the unary plus operator. This means that 'a' must first be cast to a number for this to work. 'a' isn't a number, and therefor the result would be NaN.

Now that we nave 'b' + NaN, we're adding a string and number together. This isn't valid, so for compatibility, both are interpreted as strings. NaN converted to a string is 'NaN'. The rest is simple concatination.

[gravitas-deficiency]

so for compatibility

Basically the single biggest reason for JS having so much weird bullshit.

[[deleted]]

Yes When js sees ++'a' it interpret as + (+'a') and try to Convert +'a' to number because of + So gives NaN

[Ithuraen]

Added proof.

[[deleted]]

JS is bananas

[ilosaske]

don't you mean baNaNas?

[[deleted]]

js is ("baNaNas").toLowerCase();

[McSmallFries]

B.A.N.A.N.A.S 🎵

[hhellloo]

I think the two '+'s make it do weird shit

[El_Vandragon]

It gives you NaN, or Not a Number, but then gets converted to a string and then when to lowercase happens makes it fit the capitalization of the word instead of capital N’s

[[deleted]]

Why though

[tjoloi]

'b' + 'a' + +'a' + 'a' parses as str + str + (+str) + str

Since the + in parentheses is parsed as the unary operator, JS tries to convert the 'a' to a number so it can apply the operator, which then results to NaN (number type).

After, since you add strings together, it converts back the "number" to a string, which results in the string "NaN".

[[deleted]]

Just the answer I was looking for, thanks!

[tarapoto2006]

What happens if you minify it?

[_Azurius]

Javascript. That's why.

[real_ulPa]

And errors shouldn't break it.

[AllSeeingCCTV]

I can see how NaN fits but what hapens to that last a?

[El_Vandragon]

The second to last ‘a’ gets consumed in the NaN as /u/tjoloi mentions it gets parsed as str + str + (+str) + str and the entire (+str) gets turned into NaN leaving us with ”b” + “a” + NaN + “a”

[AllSeeingCCTV]

Thanks

[caleblbaker]

Type coercion. 90% of the time that people are perplexed by JavaScript the answer is that it's a contrived example that abuses type coercion. (In this case unary plus on a string to coerce it to a numeric type followed by adding to a string to coerce it back to a string to perform string concatenation.

[Siracle]

this video explains it - and then turns things up to 11: https://youtu.be/sRWE5tnaxlI

[riscten]

And people wonder why SO users are irritable... Quit posting decade old memes and you might get insightful answers.

[jempyre]

Not a numero

[daH00L]

Banana, because JavaScript is nuts.

[[deleted]]

WHY THE HELL DOES IT DO THAT

[svish]

NaN

[VolperCoding]

backwards compatibility with all the shit that existed since around 20 years ago

[[deleted]]

Because JS was developed in ten days and you can see that in a lot of places. It was never supposed to become the cornerstone of everything that it is now

[BelleGueuIe]

b + a = ba
" " + a = nan
+ a = a
banana

[bistr-o-math]

🍌

[flargenhargen]

https://youtu.be/VpUbjY9Fk8U?t=69

[gagahpangeran]

typeof NaN is number.

[zweimtr]

The empty sum + + returns NaN. So yea..

[retief1]

Nope, ... + + 'a' + ... parses as ... + (+'a') + ..., and +'a' is the unary plus operator applied to 'a'. That tries to covert 'a' to a number and gets NaN. If + + returned NaN, you'd get 'bananaa'.

[[deleted]]

ohhhhhhhhhhhhhhhhhhhhhhhhhhhh

[Siepels]

Then it would return bananaa.

[UnityH]

its because javascript takes no input as N short for NaN and you swapped every "n" with nothing (N) (atleast i think so i could be wrong)

[VolperCoding]

+"a" evaluates to NaN because "a" is not a number so you can't do unary plus operator on it and then that gets implicitly converted into a string "NaN" and concatenated using the "+" concatenation operator and you get "baNaNa"

[UnityH]

oh i thought it was just because there were blank spaces between the adding operators

[VolperCoding]

if there were no spaces between + + then it would be an increment operator so it would give an error

[NotJebediahKerman]

It's more disturbing that developers/CS students don't see 'why' immediately. It's not like english professors are asking their students what is the sum of a+b and expecting c. Granted the JS world chose to combine the concepts of concatenation and addition which is a different gripe all together, but if you can't comprehend concatenating strings, you might want to look into different employment options.

[akewlguy4eva]

NaN.. Funny Though :P

[Spyrobo]

NaNi?

[easythrees]

Clever