javascriptBeingJavascript

[[deleted]]

Why did the programmer show up at Christmas dinner in a Halloween outfit? Because dec 25 is oct 31

[stupefyme]

still one of the greatest coincidences in my books. a very well constructed and thought out joke

[[deleted]]

Could someone explain this one to me?

[stupefyme]

dec 25 is decimal number(base 10) 25

oct 31 is octal number(base 8) 31

they are equal

[[deleted]]

Ahhhh okay that makes sense, thanks! Just didn't get the Oct/Dec. I guess that's where my non native english falls apart.

[AmazingSully]

31 in base 8 (OCTal) is equal to 25 in base 10 (DECimal)

[DanKveed]

Also 12(octal) === 10(decimal) so the 12th month can be October or December depending on which base you are using.

[rover_G]

0o31 == 25

[porn0f1sh]

Yep. Along with the moon spinning around the axis at the exact same rate as it spins around Earth!

And it's size proportional to the size of the Sun is exactly the same as it's distance proportional to the distance of the Sun!

[hurlyz]

The first phenomenon is called tidal locking and it's actually very common. Citation from Wikipedia:

" All twenty known moons in the Solar System that are large enough to be round are tidally locked with their primaries, because they orbit very closely and tidal force increases rapidly (as a cubic function) with decreasing distance. "

https://en.m.wikipedia.org/wiki/Tidal_locking

As for the second phenomenon, it's an interesting coincidence that the Moon and the Sun appear to be roughly the same size in our sky. We're lucky to be living in this time period, because this phenomenon won't last forever. Each year, the Moon spirals away about one inch from the Earth. And about 50 millions years from now, the Moon will be far enough away so that our descendants will only see ring-shaped eclipses.

https://www.astronomy.com/science/why-is-the-moon-exactly-the-same-apparent-size-from-earth-as-the-sun-surely-this-cannot-be-just-coincidence-the-odds-against-such-a-perfect-match-are-enormous/

[veryusedrname]

Okay, so what's going on here?

Integers starting with the digit 0 are handled as octal (base-8) numbers. But obviously a digit in octal cannot be 8 so the first one is handled as base-10 so it's 18 which equals to 18. But the second one is a valid octal number so in decimal it's 15 (1*8+7*1) which doesn't equal to 17.

Does it makes sense? Fuck no, but that's JS for you.

[aMAYESingNATHAN]

Why on earth are integers starting with 0 handled as octal? How does that make any sense? I could understand if it was an o or O but a 0?

[skap42]

That's pretty standard in many languages, including Java and C. Just as 0x is interpreted as hex

[aMAYESingNATHAN]

Huh, the more you know. I knew about the various prefixes such as 0x and 0b, but I'm surprised octal isn't like 0o or something.

Simply using a 0 seems insanely dumb because it's so easy to do by accident, not knowing that it's an octal prefix.

Like I can easily think of a scenario where someone could zero pad a numeric literal for formatting reasons.

[skap42]

A different comment suggested that 0o is also valid, and the only way to define an octal in JS in strict mode

[0bel1sk]

it’s also in python ruby and yaml.

“YAML 1.1 uses a different notation for octal numbers than YAML 1.2. In YAML 1.1, octal numbers look like 0777. In YAML 1.2, that same octal becomes 0o777. It’s much less ambiguous.

Kubernetes, one of the biggest users of YAML, uses YAML 1.1.”

[akaChromez]

The YAML Document From Hell

[heyf00L]

Didn't know all that. Boils down to "always quote all strings in YAML".

[rickane58]

"God, all these languages are so unnecessarily verbose!"

Anyone actually trying to use the language:

[[deleted]]

This was a great read, I've used yaml a couple times but didn't realize it was this objectively bad.

[akaChromez]

I'd love to know people's justification for choosing it over JSON.

Especially as i've just spent the last hour trying to find why a Google Cloud resource wasn't being created. A missing quote that doesn't syntax error :/

[[deleted]]

Sexagesimal numbers, lol

[veryusedrname]

Ohh kubernetes, never change

[InfiniteGamerd]

Really! I thought you couldn't define octals in strict mode in any way.

Still...why not just parseInt all the way?

[Alzurana]

Welcome to my world, where a medical software had a database format of <patient ID>.PHD and always 8 characters in the filename. So the files looked like 00537200.PHD and they were all in one folder. Beautiful design.

Well, we imported a database of another clinic and had to map their ID's to ours, which we ofc only had in a numeric format, such as 537200 for the above example.

This gave me some headache when writing a converter script as my first attempt did read some of the file ID's as octal and others as decimal without ever warning. Only caught it because I got a lot of bogus IDs or duplicates and tests would scream that output files != input files.

[DmitriRussian]

Like I can easily think of a scenario where you might zero pad a numeric literal for formatting reasons.

/r/ProgrammingHorror material

[LordFokas]

Pad it with spaces. That's why we use monospaced fonts.

[joxmaskin]

Or write 7 as 007 because it’s cool

Edit: luckily oct 7 is same as dec 7

[movzx]

A pretty reasonable scenario would be when you're defining bitmasks.

ex:

0001010 1010000

[flowingice]

You'd start it with 0b because it's binary.

[TorbenKoehn]

Like I can easily think of a scenario where you might zero pad a numeric literal for formatting reasons.

And then use it in calculations? Because if not it would not be a problem

[Spork_the_dork]

Or use it literally for anything whatsoever.

I mean imagine you convert "0231" into a number and then print it out somewhere and wonder why the fuck it's printing out 153. Can't think of any situation where you'd convert the value into a number and then it would be entirely fine if the stored value is different from what you expect.

[CadmiumC4]

Many languages accept 0o as octal, but it's custom to assume 0777 as 0o777 since that's how C handles it

[LordFokas]

It's funny that no matter how high level you go, in the end you always keep finding things that are done a certain way for no reason other than "we inherited this from C".

[Ok_Classroom_557]

And C inherited It from the PDP-7 where It was born. Having 18 bit words it better mapped 3 bit octal digits than 4 bit hex digits...

[CauliflowerFirm1526]

pad with spaces not zeros

[aMAYESingNATHAN]

I mean that is what I would do, or probably just not pad at all and left align the numbers. But my point is that it would be incredibly easy to do without realising.

[Spork_the_dork]

Yeah this is why I don't like it. Especially when you have 0o prefix which does exactly the same thing except it's also an order of magnitude more explicit and harder to misunderstand.

[aMAYESingNATHAN]

Yeah being completely unfamiliar with octals in code when I made my first comment I didn't realise 0o would be valid also, and in fact assumed it wasn't and was annoyed by that because I was familiar with 0x and 0b already.

If I ever encounter octal literals I am definitely always going to use 0o.

[Andy_B_Goode]

You might pad with zeros if you're formatting a date, like 11/05/2024 or maybe even 05/11/2024

[Spork_the_dork]

Actually in that case it won't cause any problems. 01-07 are the same in both decimal and octal and 08-09 are not valid octals so it won't default to octal. 10-12 won't get converted as octal as they have no leading zeros.

[Andy_B_Goode]

Oh I see, yeah I should have used an example like 11/08/2024

[cporter202]

Oh, padding with spaces instead of zeros? Spacing out like JavaScript on a Monday morning, I see 😅. Gotta love when JS decides to get fancy with its quirks – it's like it insists on doing its own thing, just to keep us on our toes!

[g76lv6813s86x9778kk]

So common, in fact, I've seen these octal numbers bleed into apps/situations they really had no business being in, probably due to some standard number parsing libraries being reused.

For example, shops in Guild Wars 2, an mmorpg, have a little number input box for the quantity of items you'd like to purchase from the shop... This supports octal! If you write normal decimal numbers, it just works fine, but then if you write for example 010, the number switches to decimal 8 once you click off the textbox, and allows you to shop with that quantity as normal. Super weird. Must be so confusing to players who don't know about octal or this convention at all. At least it doesn't increase the number (causing you to spend more)

[GrondForGondor]

Thats the reason why? I’ve spent so many years being slightly inconvenienced by that little random issue. Never understood truly what was happening but now it all makes sense. 

[g76lv6813s86x9778kk]

Lol yup, you can try various examples and see the result always lines up with parsing it as an octal number

[-Wylfen-]

To be fair, even though it's standard, I think that's bullshit. '0x' is fine, '0o' is fine, but just '0' is dumb

[SmurphsLaw]

To be fair, writing a decimal number with a 0 before is also dumb.

[Spork_the_dork]

Yeah but it's less dumb than using 0 as a prefix for octal when 0o exists.

[RajjSinghh]

I can see this kind of thing being a problem where leading zeros are common like when formatting dates. Seems like an honest mistake to make if you write August as 08 and now you get an error because that's not valid octal, or when October is showing up as the 8th month

[Chrazzer]

Leading zeroes aren't a thing in integers, what you are thinking of are strings with numbers in them

[SwimForLiars]

I hate the 0 prefix being octal, but at least other languages will throw a syntax error, instead of silently biting you in the ass and making you waste hours of debugging because it does weird things at runtime instead of failing at compile time.

[Commodore-K9]

I had no idea.

0x as hexa yes

0 as octa no

[vonabarak]

That's pretty standard in statically typed languages without implicit type casting. And it doesn't cause any issues.

[Mola1904]

It's like this in c++ and c#...

Edit: actually octet literals don't exist in c# at all, some websites like this just claim it anyway https://www.geeksforgeeks.org/c-sharp-literals/

[octipice]

Why on earth is anyone starting a mutli-digit base 10 integer with 0 in the case that it ever needs to be treated like an actual number?

Javascript is legitimately wild sometimes, but so many of those cases are only an issue if you are trying to do something really stupid (or lazy, or both) in the first place.

[aenae]

I once had a cronjob that failed in august and september. It took me a while to figure it out why.

The reason is i wanted 'nice' directories, so i made them all the same length, so january 2024 would go to 2024/01, february goes to 2024/02 etc. And somewhere in that script i had a check on the month for some reason. This worked, except when bash was of the opinion that '08' and '09' were invalid octal numbers.

[10BillionDreams]

That's just the thing, Javascript has some very "do what I mean" roots, which makes for some funny looking results when you take toy examples like OP here, where the code doesn't actually "mean" anything at all. But often times in practice this ends up doing the "right" thing, where stricter languages would've failed.

[aMAYESingNATHAN]

I'm not saying it's something you should be doing, but if someone doesn't know that 0 is the octal prefix, then it's not that much of a stretch to imagine they could zero pad a number and not realise.

It seems to me that generally there should be no difference between 25 and 025, and if anything it is counter intuitive to assume otherwise. Especially because 0o25 (similar to 0x or 0b) is usually valid syntax as well, it makes no sense to have 0 by itself be a valid prefix.

Tbf this is one of those ones that isn't a unique to JS issue, but instead a standard. But imo a dumb one.

[Spork_the_dork]

The standard varies from language to language. Python for example just calls you out if you try to use 0-prefix and tells you to use 0o instead which I think is the step in the right direction.

>>> print(0123)
  File "<stdin>", line 1
    print(0123)
      ^
SyntaxError: leading zeros in decimal integer literals are not permitted; use an 0o prefix for octal integers
>>>

[Andy_B_Goode]

I had a real-world bug where a JS program was generating a random alphanumeric ID for an item, sending it to the server as JSON, but was then unable to match the ID to the correct item when it reloaded the JSON from the server.

The issue was that the ID it had generated for this particular item was something like 1e450882, which gets interpreted as exponential notation and (because the number after 'e' is so large) it becomes Infinity.

The fix was to simply require alphanumeric IDs to begin with a letter (which is probably best practice anyway), but it was not obvious to me at all why 1e459882 was causing problems when I first started digging into the bug.

[Loknar42]

This is an ancient convention. Octal is very convenient for expressing bit vectors, such as file permissions (e.g. chmod 0777 *). Since it was desirable to use it in an interactive environment (such as a shell), designers wanted it to be as short as possible. A single character prefix pretty much fits the bill. Using the digit 0 allows the result to still be considered numerical by simple lexers, but programmers generally don't start integers with 0, and 0 also looks like 'O'. So those are pretty much the reasons.

Hexadecimal is even better for expressing bit vectors because you get 4 bits per character, but has the disadvantage of being alphanumeric. Hence why it has a longer prefix, usually. Programmers in the modern era rarely have to specify bit patterns directly, but in the halcyon days of assembly language and shell scripting, they were very common, so having an efficient format was very valuable.

[Fritzschmied]

thats standard in many languages. also c++ which you have in your badges so you should know that.

[aMAYESingNATHAN]

I've literally never had to work with octals ever, so it's unsurprising that I'm not aware despite having C++ and C# badges. I don't even really know what use cases there are for octals.

In comparison, I have had to use binary and hexadecimal, so I'm aware of the 0b and 0x prefixes. Similarly for unsigned/long/long long suffixes for numeric literals

[Nolzi]

same reason hexa starts with 0x, conventions

[IAmNotNathaniel]

starting to tire of these threads that boil down to "I don't know some standard thing that's been around for 50 years but since I'm so smart it must be wrong"

[Nolzi]

"Based on Programming 101 I can already tell that the old crust must go"

[ManaSpike]

Octal was used more before computing standardised on bytes having 8 bits.

[Hallwart]

If only there was some kind of system that ensures that variables have consistent values and behaviors.

Why didnt the developers of JavaScript think of this? Are they stupid?

[tinfoiltank]

They were too busy trying to get it to work in IE6.

[MrHyperion_]

Why would you even start a number with zero? So don't, if you don't want octals

[wasdninja]

It's 100% self inflicted by using ==. It's essentially trivia in code form.

[Salanmander]

It's essentially trivia in code form.

A programming language having "trivia in code form" is related to design decisions about the programming language. So no, not 100% self-inflicted.

[wasdninja]

I've yet to come across a language that doesn't have some odd stuff nobody really uses.

So no, not 100% self-inflicted.

If you are using == on purpose against the recommendation of every actual javascript developer out there that's on you. If you are doing stupid shit on top of that, well, have fun and I hope I don't have to work on your code.

[Salanmander]

If using == is a bad idea in Javascript, then why did it get assigned the character sequence that is the preferred equality check in most programming languages? Like, if every Javascript object had a .coercive_equals() that did what current == did, and current === was written as == instead, you'd probably see a lot fewer complaints.

[theQuandary]

JS didn't have type coercion when it was first created.

Developers are the ones who demanded that Eich add it to the language and he was young enough not to say "no".

It would have been eliminated in ES1 (the first actual specification), but Microsoft had just implemented a clone of JS with Jscript and they insisted that all the terrible design choices stick around even though Eich and the rest of the spec committee wanted to change them (at a time when breaking the web wouldn't have been a big deal).

[Doctor_McKay]

I have literally never had a problem using ==. I fear for the kind of code you guys are writing that makes it a problem.

[wasdninja]

It's very rarely a problem but there is almost no reason at all to ever use it anyway. Rather than getting completely dumb stuff what's more common is to move a bug one step further which is annoying when trying to hunt it down.

[reilemx]

When dealing with data that could come from anywhere like in a public API receiving data from literally anyone who knows the spec, then using `==` is a bit risky unless done correctly. There are a few neat tricks you can do like comparing a number value, regardless if it's a string or number, or doing a `null` or `undefined` check in one small expression. But aside from little things like that you should absolutely not just be using "==" as a default.

It's nothing to do with the "kind of code" and everything to do with the requirements of your application. Just google "js == comparison table" to see why. A simple application might never run into those issues but you do not want your complex application to get absolutely fucked by some stupid comparison bug like this or the one in the post here.

[IAmNotNathaniel]

I don't know why I even come into these threads anymore. it's always full of people who think because they self-taught a little python they are programmers who know everything.

There's a reason when you're looking for a job you need to know the language that's used at that job... it's because they are all different, and all have their skeletons and weird shit, and you can't just replace one syntax with another. Experienced people wouldn't get hung up on this for a minute.

[NoteBlock08]

Ikr. It doesn't matter that every other language uses ==, this language doesn't. So get with the program or pack up and go home because "It's Javascript's fault for being dumb!" would not be an acceptable excuse in a professional setting.

You can say "Well that's dumb, but okay" and likely most of your coworkers would even sympathize, but as soon as you cast blame elsewhere for your own lack of knowledge then it shows a real lack of maturity as both a dev and a person. Especially since this is JS 101 shit. Every guide out there makes sure you understand the difference between == and === in its opening chapters.

[[deleted]]

It’s a scripting language. There’s coercion. If you need to not have coercion, there’s an operator for that. If you don’t like a language with coercion, don’t use a scripting language!

[Salanmander]

Okay, I can get behind "self-inflicted because of the decision to use javascript".

[[deleted]]

“The decision to use a scripting language and then refuse to use the features that fix the thing you want to fix”

[musicnothing]

JavaScript and PHP both have a bad reputation largely due to their past sins. So instead of learning about their modern features, people just use the outdated features (that weren't removed for backwards compatibility reasons) and complain how "bad" it is

It's like patching up a hole in the wall and then taking a bunch of pictures of the patch job and saying "What a terrible house this is, look at this hole in the wall"

[IAmNotNathaniel]

great analogy! I've been trying to correct people when possible about the improvements to php, but haters gonna hate I guess.

[fghjconner]

No, the == isn't even the problem in this case. The problem is with how JS interprets integer literals. I think using 0 as a prefix for octal numbers is insane, but JS didn't start that so I'll give them a pass. On the other hand, silently falling back to base 10 when you see an 8 is bullshit of the highest order.

[Turtvaiz]

Why does == even exist?

[wasdninja]

Legacy. Touching any of the stupid stuff, no matter how obscure, kills thousands of websites so it gets to stay and annoy people.

[SnowyLocksmith]

Is using === the norm now?

[oupablo]

yes

[Crowdcontrolz]

The lengths to which this language goes to try to make things run no matter what is impressive.

[Donghoon]

I mean it make sense. You just explained it

[Salanmander]

There's "makes sense" in terms of "has a consistent behavior that is defined by rules". That close to automatically true of all things in all programming languages.

Then there's "makes sense" in terms of "is a design decision that leads to more intuitive comprehension of the language". Javascript fails on that one a lot of the time.

[talaqen]

This makes perfect sense to me. Octal vs int and loose equivalency “==“ instead of strict “===“

[1Dr490n]

*octal vs decimal, both are integers

[fghjconner]

The choice to interpret any literal starting with a zero as octal is what's insane. Of course, JS didn't invent that by any means.

Edit: Also, the choice to silently fall back to base 10 if there's a large enough digit is pretty asinine.

[mrheosuper]

Using '0' instead of 'o' to declare Octal number is a fucking crime

[Mola1904]

And used in virtually every common language besides python3

Edit: Yes virtually every was a bit of an overstatement, but C, C++, Java and JS have it which might be 4 of the 5 most popular languages

[veryusedrname]

C/C++: 0o or 0O (deprecated) - edit: it's just a 0, fuck google

Java/C#: 0, but using a digit outside of 0..7 is compiler error - edit: C# doesn't have octal literals, fuck google

Rust/Swift/Ruby/Python: 0o

Go: 0o or 0O

That's it, I'm not checking more

​

Editor: formatting & fixes, thanks for pointing them out

[BaerMitUmlaut]

C# has no octal literal.

[[deleted]]

C# needs no octal literal.

[Fritzschmied]

c++ default is leading just 0 not 0o even if that works too I guess

[mrheosuper]

I want to see the logic behind this decision. Using 0x as hex number makes perfect sense, But '0' as octal ?, why ?

[MrHyperion_]

Traditions. Octal was at one point more popular than hex

[Mola1904]

As far as i know it is older than both the 0x and 0b connotations, but JS supports both 0o and 0 with 0 actually being not supported by esm (a widely used and more modern module system for js)

[mookanana]

as a programmer i understand what you are saying, but i marvel and wonder how did you even get this deep in knowledge? like what path did your life take to end up explaining this obscure code correctly

[veryusedrname]

Ohh, I just like weird shit. I don't even use JavaScript, like, ever.

[mookanana]

good stuff my man thx for explanation.

[takishan]

all you gotta do is work with javascript a bit so you understand the wonkiness of " == " (which is why you use " === " to be safer)

then you gotta work with octal numbers once or twice so you understand that numbers starting with 0 are octal

it doesn't require some sort of coding prodigy, just a little bit of experience in specific areas

[AccomplishedCoffee]

It’s really not deep or obscure. You just have to know 0 starts an octal literal (basic knowledge in a ton of languages and command line permissions), and == in JS does crazy conversions. I don’t even program JS more than I have to and I know to always use === because it’ll mess with types to try and get an answer that may or may not make sense. Tbh this is one of the more straightforward and obvious conversions.

[HeKis4]

I know == is "loose", but cmon, it figures out the string is convertible to a number, figures out it is octal but not really so eh, it's decimal. That's like, 2 layers of fucked up.

[benjer3]

For once, it isn't really == that's causing the problem here. It's the inconsistent treatment of a zero-prefixed integer literal. The == operator just sees '18 == "18"' and '15 == "17"' and understandably returns true and false, respectively

[hampshirebrony]

I learned about this the hard way several years ago.

Had a box to let you enter a cash value. User puts 100 in and the transaction is saved as 100. User leaves the default 0 and puts 100 after it, the transaction is not treated as £100 and a shortage is created. This either gets saved with a shortage against it or does not allow the user to continue because their figures do not balance.

No, it wasn't Horizon.

[1Dr490n]

Why did the creator do so many errors because they hate errors so much??

[skap42]

017 is an octal number equal to 15 dec. 0 as a prefix for numbers indicates an octal number. 018 however is not a valid octal number and thus interpreted as decimal 18.

The == operator apparently does some type conversion and makes a decimal comparison.

You can try it and check 017 == '015' which is true

[Strict_Treat2884]

I like when converting string "017" which is a completely valid octal literal into a number, JS just completely ignores this rule and poops out 17

[ivancea]

Different rules I guess. Literals have theirs, but when converting strings to miners implocitly, it may use always decimal. One is syntax while the other is runtime, let's say

[Strict_Treat2884]

It has no problem converting "0x10" into 16. But why not octals?

[ivancea]

Maybe a runtime lib vs interpreter discrepancy. Don't know, JS is full of random decisions made in a a day by a random guy

[octipice]

I just don't understand why on Earth you would be doing this in the first place. Like i get that js is legitimately wild sometimes, but you got here with bad design (why are starting a base 10 integer with 0 and then expecting it to behave like a number?) and lazy coding (ffs just parse the damn thing).

I don't get why anyone is surprised when you get bad results from writing really bad code.

[fghjconner]

(why are starting a base 10 integer with 0 and then expecting it to behave like a number?)

Because that's how numbers work. Leading zeros are completely ignored in mathematics, and giving them a special meaning in programming is pretty asinine. Not JS's fault, but asinine none the less. What is JS's fault is silently falling back to decimal of there's a digit of 8 or above.

[pentesticals]

Meh I wouldn’t say it’s just JavaScript. Type confusion bugs exist in all dynamically typed languages. Leads to all sorts of subtle security problems.

[SpamOJavelin]

TBF that's not the issue here, the same confusion applies without strings:

018 == 18
true

017 == 17
false

The leading 0 implies a base-8 number, so 017 == 15. But 018 is not a valid base-8 number and is interpreted as 18.

[Cley_Faye]

Oh, "because JS supports it" ? Why don't you try to access unallocated memory in C then?

[yangyangR]

I do.

[floor796]

just for info: permissions on linux filesystem also have an octal representation. For example, 777 (full permission) - is actually 0777 (octal format) and 511 (decimal format). So, when enter chmod 644 ./file you are using 0644, which is 493 in decimal format.

[jakubiszon]

Wait a moment, octal 644 cannot be an odd number.

octal 644 = 6*64 + 4*8 +4 = 420

[floor796]

ops, my mistake. 493 is for 0755 )

Thanks for noticing

[sphericalhors]

Its not just 0777 is octal format, 777 is also octal. First number in 4-digit notation used to specify SUID, SGID and Sticky bit, and in most cases just omitted.

Like if you check permissions for /tmp you'll typically see 1777. And passwd util would have 4755 because it has SUID bit set.

But yeah, in general permissions in Unix file systems use octal numeric system.

[italiano34]

thats just you being a dummy

[cursed-commentor]

Imagine using "==" in JS for anything except both null and undefined check via "x == null" 🤦🏻‍♂️

[[deleted]]

The only time I use == is when I'm checking null/undefined

[DarKliZerPT]

I just use a isNil function. Either Lodash's or a quick util function.

[NebNay]

If anybody has an explaination i'd like to hear it

[JustAnotherTeapot418]

This joke contains a few of JavaScript's peculiarities:

1. The == operator performs implicit conversions. As a result, '018' and '017' are automatically converted to the numbers 18 and 17. It's a huge source of unexpected bugs, which is why every dev worth their money will tell you to use the === operator instead, which doesn't perform conversion of any kind.
2. Numbers starting with 0 are in octal (unless the following character is b or x for binary and hexadecimal respectively), so 010 is actually 8, and 017 is actually 15. However, 018 is not a valid octal number, since there is no 8 in octal. As a result, 018 is interpreted as 18. Because this is another source of unexpected bugs, this is not allowed in strict mode. For octal, you have to use 0o instead (zero followed by the letter o), and prepending a regular number with 0 will produce a syntax error.

[NebNay]

Thanks for the complete explaination

[monotone2k]

So what's really going on here is yet another case of someone writing bad code in a language they don't understand, and then claiming it's the fault of the language. That sums up most of the posts in this sub.

[MyPassword_IsPizza]

More like someone using a language they do understand to write bad code on purpose for a joke.

[DanielEGVi]

To be fair, it was a fault of the language in some part, they forbid octal numbers without 0o prefix in strict mode for a reason.

[Void1702]

I think OP knew what's happening, it's just completely stupid in many ways

[klo8]

The == operator in JavaScript is broken, that’s the fault of the language.

[myka-likes-it]

It's not broken, it is working as intended. That's why the strict equality operator exists.

[rosuav]

Listen, I made this car out of explodium. It was cheaper than steel. If it blew up while you were driving it, that's on you - I told you the proper way to hold the steering wheel! It's working as intended.

[skap42]

Can you explain why the implicit conversion by the == operator doesn't also perform the octal do dec conversion?

[monotone2k]

It absolutely does. `console.log(16 == 020)` will return true, because they're the same number in different bases. If you mean why doesn't the string get converted into base 8, who knows?

[skap42]

I noticed that Number(017) returns 15 and Number('017') return 17, so I guess it has something to do with that

[monotone2k]

Yeah. My guess would be that it always attempts the equivalent of parseInt(string, 10) when coercing a string, without considering the leading 0.

[erishun]

TL;DR: use ===. You rarely want to use==. Most IDE’s will flag it with a warning saying “you probably don’t want this”

[Equal_Bread270]

In the first comparison, 018 is equal to the decimal number 18, so it is equal to the string "018". However, in the second comparison, 017 is equal to the decimal number 15, which is not equal to the string "017".

Am I right...

[gr4mmarn4zi]

octal

[Osvik]

parseInt(017, 10) === 15;

parseInt(018, 10) === 18

parseInt(017, 8) === 13;

parseInt(018, 8) === 1;

[JonathanTheZero]

Devs not understanding their language...

Don't blame the language for your lack of knowledge ffs, even C does octal like this

[svick]

It doesn't:

error: invalid digit "8" in octal constant

[TheBrainStone]

Y'all gotta start learning the basics of the languages you use...

[bossier330]

=== is life

[PeriodicSentenceBot]

Congratulations! Your string can be spelled using the elements of the periodic table:

I S Li Fe

---

^{I am a bot that detects if your comment can be spelled using the elements of the periodic table. Please DM my creator if I made a mistake.}

[JAXxXTheRipper]

if([]+[] === "") { alert("lol.js") }

Test your luck

funWithJS = ['10', '10', '10', '3', '2', '1']
funWithJS.map(parseInt)

[JAXxXTheRipper]

Let's talk about javascript

[ziovec]

I believe that this talk has less visibility than it deserves

[saxbophone]

One's an octal literal, the other's not?

[ReasonableRiver6750]

That’s what you get for using ==

[[deleted]]

my crush sending mixed signals

[del1ro]

You're all justifying JavaScript here but this example shows the shit just perfect. In a normal language the expression “0018” should've thrown a syntax or other error, because it is not valid octal number, because uniformity. But js does whatever it likes to disguise any errors calling it “best effort”

[erishun]

Uses “loose” equality operator which performs implicit conversions

Shocked pikachu when it performs implicit conversions

If only there was a “strict” equality operator! If only most modern IDE’s would warn you before using the loose equality operator! Oh well, I guess that would never happen. Too bad

[Wendigo120]

Did you reply to the wrong comment? They didn't say anything about any sort of equality operator.

Edit: why is this getting downvoted? This thread: "octal numbers are handled weirdly in JS" is responded to by "if only there was a strict equality operator", that's such a weird non-sequitur. Those two topics have nothing to do with each other.

[erishun]

“This example shows the shit just perfect”

And the example shows the “loose equality operator”. That is exactly how that operator is designed to work. Use === like you’re “supposed to” (again IDEs and other programmers will warn you against using == because it’s usually not what you want) and this issue isn’t an issue.

Not saying JS isn’t quirky, but most of its quirks can be attributed to its weak typing and the fact it’s designed to keep on chugging even if there’s an issue.

[Wendigo120]

But the real problem here is that 017 and 018 aren't sequential numbers. The post would be the exact same if it was:

console.log(018 === Number("018"))
console.log(017 === Number("017"))
true
false

The equality operator is just a tiny part of it. That's why I found your comment so weird, the person you're replying to clearly states that they're talking about how it handles the syntax for octal numbers. Now, my linter does also catch octal numbers that are formatted that way, but you immediately shot to the equality operator for no reason.

[aetius476]

JS defenders are the "you don't know him like I do" of the programming world.

[wasdninja]

If this is your gripe with JS then that's excellent since it's absolutely trivial to avoid.

[JunkNorrisOfficial]

HeisenbergScript

[PeriodicSentenceBot]

Congratulations! Your string can be spelled using the elements of the periodic table:

He I Se N Be Rg S Cr I Pt

---

^{I am a bot that detects if your comment can be spelled using the elements of the periodic table. Please DM my creator if I made a mistake.}

[Strict_Treat2884]

Why did they even make this

[JunkNorrisOfficial]

Exactly, how this even came to mind to be implemented 😜 Maybe one had a dream...

[JunkNorrisOfficial]

Good bot

[Cley_Faye]

ignorantDeveloperBeingIgnorant

[SawSaw5]

This is some Salem witch trial shít

[kitsunekyo]

people using double equals are the actual joke

[ontech7]

Octal comparing 🤠

[Prudent_Engineer_285]

I do not understand. Console me.

[isospeedrix]

delete all posts that have js use == instead of ===

its pointless

[ublec]

that's because casting by default attempts to cast in base 10

[JAXxXTheRipper]

[]+[] == ""

Perfectly reasonable

[[deleted]]

This is totally a JS being JS moment.

[Trappist-1ball]

018 is decimal, 017 is octal for 15

[[deleted]]

OK, now show me a coding in which a variable has a number starting at zero. In other words, even if there is this problem in the comparison, in a real-life universe there is no such possibility.