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– Will Bickford2009-08-29 22:51:43 +00:00Commented Aug 29, 2009 at 22:51
- Note to future readers: This question asks one question in the body (check if a variable is either an integer or a string of digits) and a slightly different question in the title (check if a variable is a number). Which question the answers address varies, and none of the top answers correctly answer either question (except, arguably, this one, if you don't want numeric strings and NaN counts as a number). You should refer instead to the duplicate target.Ryan M– Ryan M ♦2024-08-13 10:31:10 +00:00Commented Aug 13, 2024 at 10:31
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10 Answers
The javascript function isNaN(variable) should do the trick. It returns true if the data is not a number.
4 Comments
Shog9
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.
Christoph
this will accept everything which can be converted to a number, including boolean values and
'infinity'; better use isFinite(String(foo))
nullability
Don't use isNaN, it's broken. See developer.mozilla.org/en-US/docs/JavaScript/Reference/… and use the solution proposed by @Christoph instead.
afarah
On Node,
isNaN(null) returns false.I'd go with
isFinite(String(foo)) See this answer for an explanation why. If you only want to accept integer values, look here.
6 Comments
Ryan Kirkman
Watch out for this.
isFinite(null) === true
Skystrider
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: stackoverflow.com/questions/1303646/…
Balmipour
Also returns true with an empty string, which I wouldn't consider a "number"
Luoruize
Object.prototype.toString.call(obj) === "[object Number]" will return true if passing NaN
cdosborn
Does not handle all variables:
isFinite(String(" ")) == isFinite(String("\t")) == isFinite(String("")) == true. See the answer linked. |
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?!
2 Comments
Adam Chalcraft
It's better JS style to use
typeof(something) == 'number'. With == rather than ===. Reserve === for when you really mean it.
JonnyRaa
@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" scholar.harvard.edu/files/mickens/files/towashitallaway.pdfYou 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()
Comments
function isNumeric( $probe ) { return parseFloat( String( $probe ) ) == $probe; } 
Comments
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.
1 Comment
Ryan M
Duplicate of stackoverflow.com/a/1352579 (which is also wrong), just with syntactically invalid sample code and an incorrect explanation.
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 
Comments
Be aware that empty string '' and ' ' will be considered as number by isNaN and isFinite.
Comments
You should use: $.isNumeric( i )
Comments
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"