Check for NaN, null and >=0 in one condition

Question

I have a var a;

Its value can be NaN, null and any +ve/-ve number including 0.

I require a condition which filters out all the values of a such that only >=0 values yield a true in if condition.

What is the best possible way to achieve this, I do not wish to use 3 different conditions joined using ||

Are you trying to filter nan, null, undefined and 0 values out ? — Ahmet DAL, May 10 '13 at 07:44
yes ...so that if is true only when a != Nan && a!= null and a >=0 — Bhumi Singhal, May 10 '13 at 07:47
"I do not wish to use 3 different conditions joined using ``||``" - are you ok with ``&&`` then ? What about ``+`` ? What's the purpose of such an artificial limitation ? — lqc, May 10 '13 at 08:04
@Iqc - Actually i was looking for only one condition if possible ... but i guess that is not possible .. — Bhumi Singhal, May 10 '13 at 08:12

Salman A · Answer 1 · 2013-05-10T08:10:26.697

9

typeof x == "number" && x >= 0

This works as follows:

null -- typeof null == "object" so first part of expression returns false
NaN -- typeof NaN == "number" but NaN is not greater than, less than or equal to any number including itself so second part of expression returns false
number -- any other number greater than or equal to zero the expression returns true

edited May 10 '13 at 08:10

answered May 10 '13 at 07:48

Salman A

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I don't think using `typeof` is as efficient as just checking `x !== null` – Alnitak May 10 '13 at 09:02
NaN !== null returns true. that's what OP is trying to avoid. – Hayden Holligan Jul 27 '16 at 18:37
typeof Infinity = 'number' – Vansuita Jr. Mar 28 '20 at 23:28

score 2 · Answer 2 · answered May 10 '13 at 08:35

2

I had the same problem some weeks ago, I solved it with:

if(~~Number(test1)>0) {
  //...
}

http://jsfiddle.net/pT7pp/2/

answered May 10 '13 at 08:35

RobSky

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Nice! (as long as their numbers stay in the 32-bit range) – georg May 10 '13 at 08:48
can u please explain this ? – Bhumi Singhal May 10 '13 at 09:01
Are you sure? I thought JavaScript represents numbers in double-precision (64 bit) format using IEEE-754? – RobSky May 10 '13 at 09:06
I hope it's okay to send two links for explain: http://stackoverflow.com/questions/4055633/what-does-do-in-javascript http://stackoverflow.com/questions/5971645/what-is-the-double-tilde-operator-in-javascript – RobSky May 10 '13 at 09:14
@RobSky: yes, but bitwise operators (& | ~ ^) always convert their arguments to int32's. – georg May 10 '13 at 09:22
This will cast `null` to zero then check for `>= 0` which is not desired. – Salman A May 10 '13 at 11:02

georg · Answer 3 · 2013-05-10T07:57:24.237

1

This seems to work well:

if (parseFloat(x) === Math.sqrt(x*x))...

Test:

isPositive = function(x) { return parseFloat(x) === Math.sqrt(x*x) }
a = [null, +"xx", -100, 0, 100]
a.forEach(function(x) { console.log(x, isPositive(x))})

edited May 10 '13 at 07:57

answered May 10 '13 at 07:47

georg

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score 1 · Answer 4 · answered May 10 '13 at 07:48

1

NaN is not >= 0, so the only exclusion you need to make is for null:

if (a !== null && a >= 0) {
    ...
}

answered May 10 '13 at 07:48

Alnitak

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Is there any possible way to have one condition and no conjunction(&&) – Bhumi Singhal May 10 '13 at 07:49
@BhumiSinghal not that I know of, since you require a 0 or positive answer and none of the tests for `null` will check the sign of the number. – Alnitak May 10 '13 at 07:49
2

No. Simply because you are asking two types of question: 1. Does a have a value? 2. What is the value of a? – Captain Kenpachi May 10 '13 at 07:52
This will be true if x is Infinity and I doubt the OP or most others want to accept that value – Curtis Jul 07 '18 at 06:41

Ahmet DAL · Answer 5 · 2013-05-10T08:08:31.310

1

My best solution to filter those values out would be with 2 condition and it is like;

 if(a!=undefined && a>=0){
      console.log('My variable is filtered out.')
    }

I am not sure but there is no single condition usage to make it.

edited May 10 '13 at 08:08

answered May 10 '13 at 07:48

Ahmet DAL

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fails to deny negative numbers – Alnitak May 10 '13 at 07:48
actually this will be false in case of a ==0 . Thus cant use this. – Bhumi Singhal May 10 '13 at 07:48
Yes I see. I missed something in the question. I'm sorry but as I know there is no way to do with single condition. – Ahmet DAL May 10 '13 at 07:55
and still fails to deny negative numbers – Alnitak May 10 '13 at 07:56
yes ..now this is a valid condition ...I see i will have to use two conditions in the least – Bhumi Singhal May 10 '13 at 07:58
This does not break the conditions.Because `null!=undefined` is `false`. – Ahmet DAL May 10 '13 at 08:07

score 1 · Accepted Answer · answered May 10 '13 at 09:12

1

Ohk ...But i actually found the ans .. it is so Simple .

parseInt(null) = NaN.

So if(parseInt(a)>=0){} would do ...Yayyee

answered May 10 '13 at 09:12

Bhumi Singhal

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Yes, but this also allows numeric strings like `"123"`. – georg May 10 '13 at 11:03
That is ohk in my case .. :) – Bhumi Singhal May 13 '13 at 06:54

score 0 · Answer 7 · answered May 10 '13 at 08:00

0

Since you tagged jQuery, take a look at $.isNumeric()

if($.isNumeric(a) && a >= 0)

answered May 10 '13 at 08:00

Shikiryu

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Please don't use that! "$.isNumeric("-10"); // true" - that's never a good idea. – lqc May 10 '13 at 08:01
Since this function only do a basic `return !isNaN( parseFloat(obj) ) && isFinite( obj );`, I don't understand this statement. – Shikiryu May 10 '13 at 08:04
@lqc Plus, the OP statued that `a` could only be `NaN`, `null` or a `number`. – Shikiryu May 10 '13 at 08:05
So if you know it's a number, why feed it to a parseFloat() under the covers? Also, you throw away ``+Inf``, which is a valid positive number. – lqc May 10 '13 at 08:08
@lqc I didn't statuate that *this* is the best answer (I don't think it is) but just to give a jQuery alternative. `parseFloat` validate both Integer and Float (in this case) which are Numbers. But, fair enough for `+Inf` (still I doubt he'll use it ;)) – Shikiryu May 10 '13 at 08:11

Check for NaN, null and >=0 in one condition

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