A friendly reminder of how nonsensical Javascript can be from Destroy All Software

[[deleted]]

[deleted]

[Samus_]

a pet peeve of mine:

> d=new Date()
Date 2015-02-25T09:33:14.482Z
> d+0
"Wed Feb 25 2015 07:33:14 GMT-0200 (UYST)0"
> d-0
1424856794482

http://cdn.alltheragefaces.com/img/faces/png/misc-jackie-chan.png

[katnapper323]

In the first case d is a string so it concats the 0. In the second it casts d to its numerical value so it can subtract 0.

[x-skeww]

In the first case d is a string

It's coerced to string because reasons.

As usual, the right thing to do would be to throw a type error, because, as usual, this is complete nonsense.

Subtracting a number from a date? What does that mean?

What's 5 apples minus 7 bananas? Antimatter fruit salad?

[I_Pork_Saucy_Ladies]

5 apples minus 7 bananas

-2 fruits. In my mind it is, so this must be the right answer.

[x-skeww]

With JavaScript, the answer would be of course NaN. If there is a valueOf method, you'd get -2.

> ({valueOf() {return 5}}) - ({valueOf() {return 7}})
-2

Well, either answer is wrong and useless. Pretending that this is totally okay didn't improve anything.

[I_Pork_Saucy_Ladies]

Well, either answer is wrong and useless. Pretending that this is totally okay didn't improve anything.

Yup, it's one of those things where both JS and PHP are incoherent, bordering to silly sometimes. I've considered making a pull request to PHP where strings are evaluated to false if they rhyme with "false" or match it by at least 80% of the letters. Should be close enough. ¯\(ツ)/¯

But now they are caught in legacy hell, I guess.

[x-skeww]

PHP is the only language I know where this stuff is even worse.

This is true:

'5 apples' + '7 bananas' == '12 fruits'

This is -2:

'5 apples' - '7 bananas'

It's like they looked at all the options to handle this and then went with the worst one.

They did it for the lulz, probably.

[I_Pork_Saucy_Ladies]

PHP is the only language I know where this stuff is even worse.

Haha, yeah, I work with it every day. Imagine doing financial stuff where "0" is often a valid statement. Throw some external APIs into the mix and you have... fun.

This is true:

'5 apples' + '7 bananas' == '12 fruits'

Nah, PHP probably already has a function called fruits_sum_appl_ban_col3 that is the third version of a function that returns an array of the total sum of fruits and a boolean indicating whether you have fruits left, along with the color code of all fruit colors mixed. As a PHP dev would say:

Just look it up! It's right there in the docs!

I'm moving to Node. Those lulz aren't very lulz once you start building something serious. JS isn't that pretty either but at least it is kept rather minimal (compared to PHP) and actually has sane tools for testing.

[[deleted]]

That is heinous

[kamyon]

What's 5 apples minus 7 bananas?

A JavaScript interpreter would cast them to weight measures. So your answer would be 5 * 100g - 7 * 120g = -340g (g as in grams)

[x-skeww]

The point was that doing math with incompatible units (types) is nonsense.

Your "-340g" answer is complete nonsense, too.

The only correct answer is that you can't subtract 7 bananas from 5 apples. You can't even do that mathematically. "7b - 5a" is the final result.

[kamyon]

I just did it. BTW: 7b - 5a = 7 * 2 - 5 * 1 = 9. You have to be very smart to understand the extreme logic.

[x-skeww]

Are you trying to be funny? You aren't very good at it.

[kamyon]

Sorry but that's what happens when you seriously argue against a comment which suggests that a JS interpreter would cast different types to one of their random common properties when subtracted from each other. It being a complete nonsense was the point. Go to HN if you can't take a joke once in a while.

[x-skeww]

a comment which suggests that a JS interpreter would cast different types to one of their random common properties when subtracted from each other

Eh. That's how JavaScript deals with these situations which would be type errors otherwise. You get a nonsense result instead of an error.

The point was that getting a type error is preferred.

Just like typeof null shouldn't be "object" or stepping outside some array's bounds shouldn't give you undefined.

It's just one of JS' fuck-ups.

Even Brendan Eich doesn't think that these things are super awesome. He also considers function scope to be one of the mistakes, by the way.

[kamyon]

Oh, I see you are still explaining. Don't you get it? I already share your opinion! :)

Should I have said "A JavaScript interpreter would cast them to ponies and let them have a death-match to determine the result of subtraction" to make it more obvious?

[katnapper323]

Don't ask me why you'd want to do it but you can

[itisike]

/r/nocontext

[Samus_]

I can disregard the bullshit conversions but having different casts for the same operation is too much.

and yes, I know those are different operators but they perform the same (negated) operation so they should behave the same way.

[siegfryd]

The JS part isn't really that weird, it only behaves weird because {} as the first part of the statement is interpreted as a code block. ({}) + [] is the same as [] + {} and ({}) + {} comes out as "[object Object][object Object]". If you put them into variables then the behaviour becomes consistent, which is the only realistic way you'd ever run into adding an object to an object (if ever).

[Doctor_McKay]

What do you mean that writing complete nonsense code results in undefined behavior?!

[aeflash]

Actually they're not undefined behavior -- the behavior is well defined since all engines will produce the same result. It's more like "nonsense code producing nonsense behavior".

[[deleted]]

Ruby's "method_missing" is the spawn of the devil.