Check that variable is a number

Question

How can I check that a variable is a number, either an integer or a string digit?

In PHP I could do:

if (is_int($var)) {
    echo '$var is integer';
}

Or:

if (is_numeric($var)) {
    echo '$var is numeric';
}

How can I do it in jQuery/JavaScript?

I'm assuming that you are trying to avoid a round-trip to your server to test? That would be the brain-dead-easy way ;) — Will Bickford, Aug 29 '09 at 22:51

score 45 · Answer 1 · answered Aug 29 '09 at 22:51

45

The javascript function isNaN(variable) should do the trick. It returns true if the data is not a number.

answered Aug 29 '09 at 22:51

AAA

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This is a good suggestion. FWIW, this works because strings are implicitly converted to numbers - the explicit code is: `isNaN(new Number(variable))`. Note that if you wish to restrict the code to integers, `parseInt()` will return `NaN` (testable via `isNaN()`). Be aware though that `parseInt()` will happily ignore non-numberic digits at the end of the string. – Shog9 Aug 29 '09 at 23:05
1

this will accept everything which can be converted to a number, including boolean values and `'infinity'`; better use `isFinite(String(foo))` – Christoph Aug 30 '09 at 10:43
4

Don't use isNaN, it's broken. See https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/isNaN and use the solution proposed by @Christoph instead. – nullability Mar 18 '13 at 18:52

score 27 · Accepted Answer · edited May 23 '17 at 11:46

27

I'd go with

isFinite(String(foo))

See this answer for an explanation why. If you only want to accept integer values, look here.

edited May 23 '17 at 11:46

Community

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answered Aug 30 '09 at 10:41

Christoph

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7

Watch out for this. `isFinite(null) === true` – Ryan Kirkman Sep 04 '13 at 22:58
1

isFinite("100") is true, we want to know that an object is a Number object. From my brief testing it looks like the solution here (Object.prototype.toString.call(obj) === "[object Number]") is the best: http://stackoverflow.com/questions/1303646/check-whether-variable-is-number-or-string-in-javascript – Skystrider Aug 24 '15 at 19:59
1

Also returns true with an empty string, which I wouldn't consider a "number" – Balmipour Apr 01 '17 at 23:15
Object.prototype.toString.call(obj) === "[object Number]" will return true if passing NaN – Luoruize Sep 07 '17 at 07:16
1

Does not handle all variables: `isFinite(String(" ")) == isFinite(String("\t")) == isFinite(String("")) == true`. See the answer linked. – cdosborn Jan 31 '18 at 16:58
I think `Number.isFinite()` is what you want. Behaves correctly with `null` and `''` – dlsso Jan 27 '21 at 20:00

score 13 · Answer 3 · answered Jul 14 '14 at 12:59

13

I'm pretty new to javascript but it seems like typeof(blah) lets you check if something is a number (it doesn't say true for strings). A know the OP asked for strings + numbers but I thought this might be worth documenting for other people.

eg:

function isNumeric(something){
    return typeof(something) === 'number';
}

Here are the docs

and here's a few console runs of what typeof produces:

typeof(12);
"number"
typeof(null);
"object"
typeof('12');
"string"
typeof(12.3225);
"number"

one slight weirdness I am aware of is

typeof(NaN);
"number"

but it wouldn't be javascript without something like that right?!

answered Jul 14 '14 at 12:59

JonnyRaa

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1

It's better JS style to use `typeof(something) == 'number'`. With `==` rather than `===`. Reserve `===` for when you really mean it. – Adam Chalcraft Feb 22 '20 at 23:35
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@AdamChalcraft most linters/programmers would probably disagree and say the opposite - always use `===` unless there's a good reason not to, if you'll get into the habit of using `==` you'll get burned by something bizaare happening at some point. In this case there's no type coercion going on so it's a fairly moot point either way. For an educational (and also hilarious) rant on the topic check out James Mickens' "To wash it all away" http://scholar.harvard.edu/files/mickens/files/towashitallaway.pdf – JonnyRaa Mar 02 '20 at 12:57

Mechisso · Answer 4 · 2018-11-01T18:01:30.967

4

You should use:

if(Number.isInteger(variable))
   alert("It is an integer");
else
   alert("It is not a integer");

you can find the reference in: Number.isInteger()

edited Nov 01 '18 at 18:01

answered Mar 28 '18 at 11:12

Mechisso

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score 1 · Answer 5 · answered Aug 29 '09 at 22:59

1

function isNumeric( $probe )
{
    return parseFloat( String( $probe ) ) == $probe;
}

answered Aug 29 '09 at 22:59

Decent Dabbler

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score 1 · Answer 6 · edited Jul 14 '14 at 13:10

1

You should use:

var x = 23;
var y = 34hhj;

isNaN(x); 
isNaN(y);

It will return true if its string and false if its a number.

edited Jul 14 '14 at 13:10

Paresh Mayani

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answered Jul 14 '14 at 13:07

Kuldeep Singh

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score 0 · Answer 7 · answered Aug 20 '15 at 05:37

You should use

simple way to check whether given value is number by using "if condition"

function isInteger(value)      
{       
    num=value.trim();         
    return !(value.match(/\s/g)||num==""||isNaN(num)||(typeof(value)=='number');        
}

it will return true if the value which we are passing is an integer..

solved for     
value=""      //false null     
value="12"    //true only integers       
value="a"     //false     
value=" 12"   //false      
value="12 "   //false         
value=" "     //false space        
value="$12"   //false special characters 
value="as12"    //false

score 0 · Answer 8 · answered Feb 29 '16 at 11:20

0

Be aware that empty string '' and ' ' will be considered as number by isNaN and isFinite.

answered Feb 29 '16 at 11:20

AnomalySmith

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score 0 · Answer 9 · edited Sep 23 '16 at 08:04

0

You should use: $.isNumeric( i )

jQuery.isNumeric API

edited Sep 23 '16 at 08:04

Petter Friberg

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answered Sep 23 '16 at 08:01

FenixAdar

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score 0 · Answer 10 · answered Sep 17 '21 at 07:08

The typeof operator returns a string indicating the type of the unevaluated operand.

const num = 42;
console.log(typeof num === "number"); // expected return true
if(typeof num === "number"){
   console.log("This is number")
}

More on it......

console.log(typeof 42);
// expected output: "number"

console.log(typeof 'blubber');
// expected output: "string"

console.log(typeof true);
// expected output: "boolean"

console.log(typeof undeclaredVariable);
// expected output: "undefined"

Check that variable is a number

10 Answers10

More on it......

Linked