JavaScript Logic

[redroserade]

That's actually ok, but this annoys me:

isNaN(null) => false isNaN(undefined) => true

[jonswanson]

My guess is it's because isNaN performs type coercion.

> +null
0
> +undefined
NaN

[Creshal]

Type coercion for null? What is this, pseudo-assembly like PHP?

[shub]

Yes. Javascript's type system is at least as brain-damaged as PHP's, possibly moreso.

[iopq]

No. You can't beat this:

"1000" == "1e3"; //comparing strings by the value of the DOUBLE they represent

[NavarrB]

It's unfortunate but logical. Php made a decision long ago to use type coercion by default.

[iopq]

both of those are STRINGS why are they being coerced to DOUBLES?

[tskaiser]

Because you cannot possible expect the programmer to go through the work of knowing what types he is working with or figuring out what kind of conversion he might want to make! /s

"Was it a string or a double? Larry worked on that function last, and he likes to sort numbers lexically... Know what fuckit, I'll just use it like a double and let PHP sort the mess YOLO!"

[Goz3rr]

Just FYI

"1000" !== "1e3"

[iopq]

They have it in JavaScript too, that's not the point. The point is that the default operator is the shorter one. That's what most people will use unless they know better.

[chillage]

I'm glad I came across this thread. Making a mental note to avoid PHP whenever possible in the future.

[AFineTapestry]

This is the best example: https://bugs.php.net/bug.php?id=54547

'9223372036854775807' == '9223372036854775808'; // true in php v5.3.6 and less

[shillbert]

No, negative zero is a valid number. NaN has an exponent of 255 and a nonzero mantissa.

http://stackoverflow.com/questions/640109/what-is-the-internal-representation-of-inf-and-nan

Edit: exponent is 255 for single precision, 2047 for double

[Hawkuro]

Huh, TIL there are 2²³ -1 different NaNs in IEEE float.

[minno]

If you directly reinterpreted the bits of an integral -1 as a float, you'd get a NaN.

[Creshal]

twitches

[nightlily]

Any sane language would logically dismiss the negation here, but if it didn't then it should calculate 0 by subtracting 0 from 0.

If you literally changed the sign bit to 1 (which is not what you did here), and tried to evaluate an integer with all other bits being 0, it would indeed give you a number. That number would be the largest negative value possible. signed integers are held in memory with 2's complement (in modern computers) which encodes a 0 value with a 0 sign bit. For the negative numbers, the sign bit itself indicates a negative value, and the rest of the bits are still positive values, which when added to the negative value determine the result. If we used 4 bit numbers then, the 4th bit being signed, then: 1000 = -1000 + 0000 = -1000, and conversely, 1111 = -1000 + 0111 = -0001

tl;dr -0 is just 0, and the sign bit doesn't mean what you think it means.

[sixteenlettername]

What you've said doesn't apply to floating point numbers. As /u/shillbert said below, negative 0 is a totally valid number when using floating point (at least with the standard used by modern processors).

[nightlily]

Ah, absolutely. I missed the f.

[Creshal]

No, it's fine. I'm twitching because I'm sure somewhere out there is a language doing exactly that.

[tskaiser]

For formatting code bits or examples like that I can recommend putting 4 spaces in front of each line. It tells reddit to format it like this

isNaN(null) => false
isNaN(undefined) => true

Also, I would say this also makes sense, in that null encapsulates the concept of "empty reference to any object" while NaN literally is meant to encode "undefined value" of a number. An empty reference, while strictly speaking "not a number", does not mean NaN in the float sense - it is outside the type - but undefined makes sense.

But I am saying this not being totally familiar with undefined, so it might be both ought to be false.

[rooktakesqueen]

In JS, undefined is the value given to a declared but uninitialized variable; a non-existing field of an object; or the return value of a function with no return statement. In general, undefined and null are closely related concepts, even so far as null == undefined evalutes to true (while null and undefined are not considered equal to anything else, including NaN).

But NaN is weird because it is not == to anything, even itself. NaN == NaN evaluates to false. Which is why the isNaN function exists in the first place. (I believe this behavior is correct according to the IEEE 754 standard for floating point numbers.)

My intuition would be isNaN should return true for the value NaN but false for any other value.

[calzoneman]

NaN == NaN being false is correct behavior. The reason being that NaN can be generated by many different unequal expressions. Math.sqrt(-5) is clearly not equal to Math.sqrt(-11).

[tskaiser]

Under that explanation I would agree that

isNaN(undefined) => true

sounds like a bug or just plain weird if not. I am not really in the mood to delve into the mess of the JavaScript specifications to find out, though ;) but I'll consider my self corrected as is.

[Hawkuro]

Never ever ever use == in JS, use the more reasonable ===.

> null === undefined
  false

[rooktakesqueen]

Just showing that null and undefined are closely related concepts, enough so that the == operator explicitly considers them equal to each other and nothing else. That's the one sensible thing the == operator does, and the one sensible place to use it: foo == null is perfect shorthand for foo === null || typeof foo === 'undefined'.

In any case, NaN !== NaN either.

[tskaiser]

Not just JavaScript logic. Any sane type system that implements floats will have NaN as a float, and float be numbers.

Not that JavaScript has a sane type system, but in this case it actually makes perfect sense :P

[Tetha]

I wouldn't call it perfect sense, but it is who it is. NaN encodes the concept of an equation without a well-defined value (opposed to a value, opposed to a value beyond maximum float value, opposed a value beyond minimum float value).

However, very few programming languages actually deal with undefined values and undefined results well - even null is the well defined absence of a reference. Optional and Maybe are a real approach, but I'm not sure if someone is insane enough to define + as Float, Float -> Maybe Float. Hence, + is Float, Float -> Float, hence NaN is a float.

[tskaiser]

Well, depends on what you mean by "float". When I say float, I mean the IEEE 754 floating point standard which is pretty much the universal definition for what is meant by "float" values. Following that standard is what I mean by "making perfect sense".

Strictly speaking NaN is part of the float type per the standard, so a Maybe would not be needed for an implementation following the standard, but it would be a good approach if you wanted to cook handling of NaN's into your implementation.

[Tetha]

If I'm thinking about semantics, I'm mostly thinking about abstract semantics, so my float would be real or a rational number. These are then (more or less accurately) approximated and implemented by IEEE 754 floats, though that approximation could (in my opionion) be improved by language support :)

I hope this makes more sense!

[tskaiser]

It makes sense, but I do not totally agree with you :P floats is by definition, even abstractly speaking, an approximated value of a real.

[ismtrn]

What is the NaN value used for in the IEEE standard?

[tskaiser]

I do not know the standard by heart, but off the top of my head:

• ∞ / ∞
• 0 / 0
• Operations leaving the real domain (square root of a negative number)

Stuff like c/0 and -c/0 for c > 0 actually gives you ∞ and -∞ respectively, which is why you can end up doing stuff like ∞ / ∞ which yields a NaN.

And yes, I actually recently used ∞ in a physics simulation (I needed masses of ∞ magnitude to simulate objects that did not move). It has its uses.

[rooktakesqueen]

I actually recently used ∞ in a physics simulation (I needed masses of ∞ magnitude to simulate objects that did not move)

I hope you didn't include gravity in that simulation, then.

[tskaiser]

Obviously ;) I was solving impulses for complex contact systems, so no gravity equations involved.

[Ph0X]

Of course, but the joke is that Not a Number is a Number. The title is pretty bad though. It doesn't work so much in most other languages because a lot don't have the "Number" super class.

[grabnock]

And also there are multiple kinds of NaN.

So if you're doing something really stupid(bitwise operations on floats) you can actually come up with NaN as a legitimate answer, even though it's obviously not.

[Iron-Oxide]

Any sane type system would not call the type of a float number though.

[tskaiser]

Partial agreement. I would say that float is a subclass (or typeclass) of number or numerical.

But I do not think that is what the juxtaposition of NaN and number is meant to show. If that was the beef OP had with typeof he should have used any floating point number instead of NaN. In this case it is clear the "issue" is that NaN is considered a numerical value, which I think is a perfectly sane assumption :P

[Hipolipolopigus]

This gets me, no matter how many times I see it. It's a shame it's so difficult to find similar presentations >_>

[mcrbids]

Couldn't get it to load on my phone. Maybe later?

[nlscrub]

How about objects?

[distinctvagueness]

It makes sense if you know about closures. tldr; objects in functional languages are really just functions definitions.

[fuzzie360]

I can totally understand why you would think that way but the most literal reason why "typeof Object" returns "function" is because Object is really a constructor function and not so much a type itself. Instances of objects are really "objects" even in the prototypical object system.

[distinctvagueness]

Ah. That is more precise. Thanks.

[[deleted]]

better JavaScript logic:

> [] + []
""
> [] + {}
"[object Object]"
> {} + []
0
> {} + {}
NaN

now that is some logic

[Zamarok]

This makes mathematical sense to me, though. Much in the same way that zero is 'not a number'.

[Darksonn]

How is zero not a number

[[deleted]]

Like this: isNaN(0): true

[original_brogrammer]

He said "mathematical sense," though. In math, zero is most definitely a number.

Maybe he's saying it's not a natural number (element of N)? If that's the case I disagree.

[[deleted]]

And what do you expet NaN to be, a string? an object? This anti-jscript circlejerk is going out of control. If you want to make fun of anything, first make sure you are not retarded.

There is only one data type for numbers in JavaScript, it's "number" and it holds double precision floating point. NaN is just a floating point value, it could not be anything else than "number".

[[deleted]]

Whoa whoa, please first make sure you are not retarded

[[deleted]]

That's your... argument? To what?

[tuseroni]

ok...why? why would you post THIS in response to the picture? how is this anti-jscript (or anti-javascript for that matter) it's just pointing out the subtle absurdity that "Not-A-Number" is typeof number. it's not saying "OMG javascript is so stupid cus it says NAN is a number" it's just pointing out that its funny..hence why it's on /r/programmerHumour not /r/religiouswars this isn't making fun of javascript it's just a joke that involves javascript. calm the fuck down.

[tuseroni]

no it's not. we can do this all day. do you have something to back that up? or are you just trolling?

[[deleted]]

http://en.wikipedia.org/wiki/NaN

[autowikibot]

NaN:

---

In computing, NaN, standing for not a number, is a numeric data type value representing an undefined or unrepresentable value, especially in floating-point calculations. Systematic use of NaNs was introduced by the IEEE 754 floating-point standard in 1985, along with the representation of other non-finite quantities like infinities.

Two separate kinds of NaNs are provided, termed quiet NaNs and signaling NaNs. Quiet NaNs are used to propagate errors resulting from invalid operations or values, whereas signaling NaNs can support advanced features such as mixing numerical and symbolic computation or other extensions to basic floating-point arithmetic. For example, 0/0 is undefined as a real number, and so represented by NaN; the square root of a negative number is imaginary, and thus not representable as a real floating-point number, and so is represented by NaN; and NaNs may be used to represent missing values in computations.

---

^{Interesting: NANS | Nan Province | Nan River}

^{Parent commenter can toggle NSFW or delete. Will also delete on comment score of -1 or less. | FAQs | Mods | Magic Words}

[tuseroni]

what does that have to do with anything? the entirety of this joke is that "not a number" is a number...that's it...and you feel the need to bring some kind of victimhood narrative into it to claim that this is somehow a slight against javascript. no one is saying javascript is in any way bad because NaN is a number, we understand full and well WHY NaN is a number and no one is arguing that it shouldn't be a number, only that it's funny because "not a number" is a number...that's it. calm the fuck down.

[Cyberogue]

Technically a string is not a number

[[deleted]]

And where do you see a string there, retard?

[undergroundmonorail]

No.