[javascript] Validate decimal numbers in JavaScript - IsNumeric()

What's the cleanest, most effective way to validate decimal numbers in JavaScript?

Bonus points for:

1. Clarity. Solution should be clean and simple.
2. Cross-platform.

Test cases:

01. IsNumeric('-1')      => true
02. IsNumeric('-1.5')    => true
03. IsNumeric('0')       => true
04. IsNumeric('0.42')    => true
05. IsNumeric('.42')     => true
06. IsNumeric('99,999')  => false
07. IsNumeric('0x89f')   => false
08. IsNumeric('#abcdef') => false
09. IsNumeric('1.2.3')   => false
10. IsNumeric('')        => false
11. IsNumeric('blah')    => false

I'd like to add the following:

1. IsNumeric('0x89f') => true
2. IsNumeric('075') => true

Positive hex numbers start with 0x and negative hex numbers start with -0x. Positive oct numbers start with 0 and negative oct numbers start with -0. This one takes most of what has already been mentioned into consideration, but includes hex and octal numbers, negative scientific, Infinity and has removed decimal scientific (4e3.2 is not valid).

function IsNumeric(input){
  var RE = /^-?(0|INF|(0[1-7][0-7]*)|(0x[0-9a-fA-F]+)|((0|[1-9][0-9]*|(?=[\.,]))([\.,][0-9]+)?([eE]-?\d+)?))$/;
  return (RE.test(input));
}

knockoutJs Inbuild library validation functions

By extending it the field get validated

1) number

self.number = ko.observable(numberValue).extend({ number: true});

TestCase

numberValue = '0.0'    --> true
numberValue = '0'      --> true
numberValue = '25'     --> true
numberValue = '-1'     --> true
numberValue = '-3.5'   --> true
numberValue = '11.112' --> true
numberValue = '0x89f'  --> false
numberValue = ''       --> false
numberValue = 'sfsd'   --> false
numberValue = 'dg##$'  --> false

2) digit

self.number = ko.observable(numberValue).extend({ digit: true});

TestCase

numberValue = '0'      --> true
numberValue = '25'     --> true
numberValue = '0.0'    --> false
numberValue = '-1'     --> false
numberValue = '-3.5'   --> false
numberValue = '11.112' --> false
numberValue = '0x89f'  --> false
numberValue = ''       --> false
numberValue = 'sfsd'   --> false
numberValue = 'dg##$'  --> false

3) min and max

self.number = ko.observable(numberValue).extend({ min: 5}).extend({ max: 10});

This field accept value between 5 and 10 only

TestCase

numberValue = '5'    --> true
numberValue = '6'    --> true
numberValue = '6.5'  --> true
numberValue = '9'    --> true
numberValue = '11'   --> false
numberValue = '0'    --> false
numberValue = ''    --> false

If you need to validate a special set of decimals y you can use this simple javascript:

http://codesheet.org/codesheet/x1kI7hAD

<input type="text" name="date" value="" pattern="[0-9]){1,2}(\.){1}([0-9]){2}" maxlength="6" placeholder="od npr.: 16.06" onchange="date(this);" />

The Javascript:

function date(inputField) {        
  var isValid = /^([0-9]){1,2}(\.){1}([0-9]){2}$/.test(inputField.value);   
  if (isValid) {
    inputField.style.backgroundColor = '#bfa';
  } else {
    inputField.style.backgroundColor = '#fba';
  }
  return isValid;
}

$('.rsval').bind('keypress', function(e){  
        var asciiCodeOfNumbers = [48,46, 49, 50, 51, 52, 53, 54, 54, 55, 56, 57];
        var keynum = (!window.event) ? e.which : e.keyCode; 
        var splitn = this.value.split("."); 
        var decimal = splitn.length;
        var precision = splitn[1]; 
        if(decimal == 2 && precision.length >= 2  ) { console.log(precision , 'e');   e.preventDefault(); } 
        if( keynum == 46 ){  
            if(decimal > 2) { e.preventDefault(); }  
        } 
        if ($.inArray(keynum, asciiCodeOfNumbers) == -1)
            e.preventDefault();    
  });

Since jQuery 1.7, you can use jQuery.isNumeric():

$.isNumeric('-1');      // true
$.isNumeric('-1.5');    // true
$.isNumeric('0');       // true
$.isNumeric('0.42');    // true
$.isNumeric('.42');     // true
$.isNumeric('0x89f');   // true (valid hexa number)
$.isNumeric('99,999');  // false
$.isNumeric('#abcdef'); // false
$.isNumeric('1.2.3');   // false
$.isNumeric('');        // false
$.isNumeric('blah');    // false

Just note that unlike what you said, 0x89f is a valid number (hexa)

You can minimize this function in a lot of way, and you can also implement it with a custom regex for negative values or custom charts:

$('.number').on('input',function(){
    var n=$(this).val().replace(/ /g,'').replace(/\D/g,'');
    if (!$.isNumeric(n))
        $(this).val(n.slice(0, -1))
    else
        $(this).val(n)
});

An integer value can be verified by:

function isNumeric(value) {
    var bool = isNaN(+value));
    bool = bool || (value.indexOf('.') != -1);
    bool = bool || (value.indexOf(",") != -1);
    return !bool;
};

This way is easier and faster! All tests are checked!

Well, I'm using this one I made...

It's been working so far:

function checkNumber(value) {
    if ( value % 1 == 0 )
        return true;
    else
        return false;
}

If you spot any problem with it, tell me, please.

Like any numbers should be divisible by one with nothing left, I figured I could just use the module, and if you try dividing a string into a number the result wouldn't be that. So.

I have run the following below and it passes all the test cases...

It makes use of the different way in which parseFloat and Number handle their inputs...

function IsNumeric(_in) {
    return (parseFloat(_in) === Number(_in) && Number(_in) !== NaN);
}

The following may work as well.

function isNumeric(v) {
         return v.length > 0 && !isNaN(v) && v.search(/[A-Z]|[#]/ig) == -1;
   };

@Zoltan Lengyel 'other locales' comment (Apr 26 at 2:14) in @CMS Dec answer (2 '09 at 5:36):

I would recommend testing for typeof (n) === 'string':

    function isNumber(n) {
        if (typeof (n) === 'string') {
            n = n.replace(/,/, ".");
        }
        return !isNaN(parseFloat(n)) && isFinite(n);
    }

This extends Zoltans recommendation to not only be able to test "localized numbers" like isNumber('12,50') but also "pure" numbers like isNumber(2011).

Here's a lil bit improved version (probably the fastest way out there) that I use instead of exact jQuery's variant, I really don't know why don't they use this one:

function isNumeric(val) {
    return !isNaN(+val) && isFinite(val);
}

The downside of jQuery's version is that if you pass a string with leading numerics and trailing letters like "123abc" the parseFloat | parseInt will extract the numeric fraction out and return 123, BUT, the second guard isFinite will fail it anyway. With the unary + operator it will die on the very first guard since + throws NaN for such hybrids :) A little performance yet I think a solid semantic gain.

@CMS' answer: Your snippet failed on whitespace cases on my machine using nodejs. So I combined it with @joel's answer to the following:

is_float = function(v) {
    return !isNaN(v) && isFinite(v) &&
        (typeof(v) == 'number' || v.replace(/^\s+|\s+$/g, '').length > 0);
}

I unittested it with those cases that are floats:

var t = [
        0,
        1.2123,
        '0',
        '2123.4',
        -1,
        '-1',
        -123.423,
        '-123.432',
        07,
        0xad,
        '07',
        '0xad'
    ];

and those cases that are no floats (including empty whitespaces and objects / arrays):

    var t = [
        'hallo',
        [],
        {},
        'jklsd0',
        '',
        "\t",
        "\n",
        ' '
    ];

Everything works as expected here. Maybe this helps.

Full source code for this can be found here.

function IsNumeric(num) {
     return (num >=0 || num < 0);
}

This works for 0x23 type numbers as well.

My solution,

function isNumeric(input) {
    var number = /^\-{0,1}(?:[0-9]+){0,1}(?:\.[0-9]+){0,1}$/i;
    var regex = RegExp(number);
    return regex.test(input) && input.length>0;
}

It appears to work in every situation, but I might be wrong.

Use the function isNaN. I believe if you test for !isNaN(yourstringhere) it works fine for any of these situations.

I think my code is perfect ...

/**_x000D_
 * @param {string} s_x000D_
 * @return {boolean}_x000D_
 */_x000D_
var isNumber = function(s) {_x000D_
    return s.trim()!=="" && !isNaN(Number(s));_x000D_
};

Here I've collected the "good ones" from this page and put them into a simple test pattern for you to evaluate on your own.

For newbies, the console.log is a built in function (available in all modern browsers) that lets you output results to the JavaScript console (dig around, you'll find it) rather than having to output to your HTML page.

var isNumeric = function(val){
    // --------------------------
    // Recommended
    // --------------------------

    // jQuery - works rather well
    // See CMS's unit test also: http://dl.getdropbox.com/u/35146/js/tests/isNumber.html
    return !isNaN(parseFloat(val)) && isFinite(val);

    // Aquatic - good and fast, fails the "0x89f" test, but that test is questionable.
    //return parseFloat(val)==val;

    // --------------------------
    // Other quirky options
    // --------------------------
    // Fails on "", null, newline, tab negative.
    //return !isNaN(val);

    // user532188 - fails on "0x89f"
    //var n2 = val;
    //val = parseFloat(val);
    //return (val!='NaN' && n2==val);

    // Rafael - fails on negative + decimal numbers, may be good for isInt()?
    // return ( val % 1 == 0 ) ? true : false;

    // pottedmeat - good, but fails on stringy numbers, which may be a good thing for some folks?
    //return /^-?(0|[1-9]\d*|(?=\.))(\.\d+)?$/.test(val);

    // Haren - passes all
    // borrowed from http://www.codetoad.com/javascript/isnumeric.asp
    //var RE = /^-{0,1}\d*\.{0,1}\d+$/;
    //return RE.test(val);

    // YUI - good for strict adherance to number type. Doesn't let stringy numbers through.
    //return typeof val === 'number' && isFinite(val);

    // user189277 - fails on "" and "\n"
    //return ( val >=0 || val < 0);
}

var tests = [0, 1, "0", 0x0, 0x000, "0000", "0x89f", 8e5, 0x23, -0, 0.0, "1.0", 1.0, -1.5, 0.42, '075', "01", '-01', "0.", ".0", "a", "a2", true, false, "#000", '1.2.3', '#abcdef', '', "", "\n", "\t", '-', null, undefined];

for (var i=0; i<tests.length; i++){
    console.log( "test " + i + ":    " + tests[i] + "    \t   " + isNumeric(tests[i]) );
}

I found simple solution, probably not best but it's working fine :)

So, what I do is next, I parse string to Int and check if length size of new variable which is now int type is same as length of original string variable. Logically if size is the same it means string is fully parsed to int and that is only possible if string is "made" only of numbers.

var val=1+$(e).val()+'';
var n=parseInt(val)+'';
if(val.length == n.length )alert('Is int');

You can easily put that code in function and instead of alert use return true if int. Remember, if you use dot or comma in string you are checking it's still false cos you are parsing to int.

Note: Adding 1+ on e.val so starting zero wouldn't be removed.

This should work. Some of the functions provided here are flawed, also should be faster than any other function here.

        function isNumeric(n)
        {
            var n2 = n;
            n = parseFloat(n);
            return (n!='NaN' && n2==n);
        }

Explained:

Create a copy of itself, then converts the number into float, then compares itself with the original number, if it is still a number, (whether integer or float) , and matches the original number, that means, it is indeed a number.

It works with numeric strings as well as plain numbers. Does not work with hexadecimal numbers.

Warning: use at your own risk, no guarantees.

A simple and clean solution by leveraging language's dynamic type checking:

function IsNumeric (string) {
   if(string === ' '.repeat(string.length)){
     return false
   }
   return string - 0 === string * 1
}

if you don't care about white-spaces you can remove that " if "

see test cases below

function IsNumeric (string) {_x000D_
   if(string === ' '.repeat(string.length)){_x000D_
      return false_x000D_
   }_x000D_
   return string - 0 === string * 1_x000D_
}_x000D_
_x000D_
_x000D_
console.log('-1' + ' ? ' + IsNumeric('-1'))    _x000D_
console.log('-1.5' + ' ? ' + IsNumeric('-1.5')) _x000D_
console.log('0' + ' ? ' + IsNumeric('0'))     _x000D_
console.log('0.42' + ' ? ' + IsNumeric('0.42'))   _x000D_
console.log('.42' + ' ? ' + IsNumeric('.42'))    _x000D_
console.log('99,999' + ' ? ' + IsNumeric('99,999'))_x000D_
console.log('0x89f' + ' ? ' + IsNumeric('0x89f'))  _x000D_
console.log('#abcdef' + ' ? ' + IsNumeric('#abcdef'))_x000D_
console.log('1.2.3' + ' ? ' + IsNumeric('1.2.3')) _x000D_
console.log('' + ' ? ' + IsNumeric(''))    _x000D_
console.log('33 ' + ' ? ' + IsNumeric('33 '))

function isNumeric(n) {
    var isNumber = true;

    $.each(n.replace(/ /g,'').toString(), function(i, v){
        if(v!=',' && v!='.' && v!='-'){
            if(isNaN(v)){
               isNumber = false;
               return false;
            }
         }
     });

    return isNumber;
}

isNumeric(-3,4567.89);   // true <br>

isNumeric(3,4567.89);   // true <br>

isNumeric("-3,4567.89");   // true <br>

isNumeric(3d,4567.89);   // false

return (input - 0) == input && input.length > 0;

didn't work for me. When I put in an alert and tested, input.length was undefined. I think there is no property to check integer length. So what I did was

var temp = '' + input;
return (input - 0) == input && temp.length > 0;

It worked fine.

function inNumeric(n){
   return Number(n).toString() === n;
}

If n is numeric Number(n) will return the numeric value and toString() will turn it back to a string. But if n isn't numeric Number(n) will return NaN so it won't match the original n

I'm using simpler solution:

function isNumber(num) {
    return parseFloat(num).toString() == num
}

The following seems to works fine for many cases:

function isNumeric(num) {
    return (num > 0 || num === 0 || num === '0' || num < 0) && num !== true && isFinite(num);
}

This is built on top of this answer (which is for this answer too): https://stackoverflow.com/a/1561597/1985601

Yahoo! UI uses this:

isNumber: function(o) {
    return typeof o === 'number' && isFinite(o);
}

One can use a type-check library like https://github.com/arasatasaygin/is.js or just extract a check snippet from there (https://github.com/arasatasaygin/is.js/blob/master/is.js#L131):

is.nan = function(value) {    // NaN is number :) 
  return value !== value;
};
 // is a given value number?
is.number = function(value) {
    return !is.nan(value) && Object.prototype.toString.call(value) === '[object Number]';
};

In general if you need it to validate parameter types (on entry point of function call), you can go with JSDOC-compliant contracts (https://www.npmjs.com/package/bycontract):

/**
 * This is JSDOC syntax
 * @param {number|string} sum
 * @param {Object.<string, string>} payload
 * @param {function} cb
 */
function foo( sum, payload, cb ) {
  // Test if the contract is respected at entry point
  byContract( arguments, [ "number|string", "Object.<string, string>", "function" ] );
}
// Test it
foo( 100, { foo: "foo" }, function(){}); // ok
foo( 100, { foo: 100 }, function(){}); // exception

None of the answers return false for empty strings, a fix for that...

function is_numeric(n)
{
 return (n != '' && !isNaN(parseFloat(n)) && isFinite(n));
}

I realize this has been answered many times, but the following is a decent candidate which can be useful in some scenarios.

it should be noted that it assumes that '.42' is NOT a number, and '4.' is NOT a number, so this should be taken into account.

function isDecimal(x) {
  return '' + x === '' + +x;
}

function isInteger(x) {
  return '' + x === '' + parseInt(x);
}

The isDecimal passes the following test:

function testIsNumber(f) {
  return f('-1') && f('-1.5') && f('0') && f('0.42')
    && !f('.42') && !f('99,999') && !f('0x89f')
    && !f('#abcdef') && !f('1.2.3') && !f('') && !f('blah');
}

The idea here is that every number or integer has one "canonical" string representation, and every non-canonical representation should be rejected. So we cast to a number and back, and see if the result is the original string.

Whether these functions are useful for you depends on the use case. One feature is that distinct strings represent distinct numbers (if both pass the isNumber() test).

This is relevant e.g. for numbers as object property names.

var obj = {};
obj['4'] = 'canonical 4';
obj['04'] = 'alias of 4';
obj[4];  // prints 'canonical 4' to the console.

No need to use extra lib.

const IsNumeric = (...numbers) => {
  return numbers.reduce((pre, cur) => pre && !!(cur === 0 || +cur), true);
};

Test

> IsNumeric(1)
true
> IsNumeric(1,2,3)
true
> IsNumeric(1,2,3,0)
true
> IsNumeric(1,2,3,0,'')
false
> IsNumeric(1,2,3,0,'2')
true
> IsNumeric(1,2,3,0,'200')
true
> IsNumeric(1,2,3,0,'-200')
true
> IsNumeric(1,2,3,0,'-200','.32')
true

It can be done without RegExp as

function IsNumeric(data){
    return parseFloat(data)==data;
}

I think parseFloat function can do all the work here. The function below passes all the tests on this page including isNumeric(Infinity) == true:

function isNumeric(n) {

    return parseFloat(n) == n;
}

Here's a dead-simple one (tested in Chrome, Firefox, and IE):

function isNumeric(x) {
  return parseFloat(x) == x;
}

Test cases from question:

console.log('trues');
console.log(isNumeric('-1'));
console.log(isNumeric('-1.5'));
console.log(isNumeric('0'));
console.log(isNumeric('0.42'));
console.log(isNumeric('.42'));

console.log('falses');
console.log(isNumeric('99,999'));
console.log(isNumeric('0x89f'));
console.log(isNumeric('#abcdef'));
console.log(isNumeric('1.2.3'));
console.log(isNumeric(''));
console.log(isNumeric('blah'));

Some more test cases:

console.log('trues');
console.log(isNumeric(0));
console.log(isNumeric(-1));
console.log(isNumeric(-500));
console.log(isNumeric(15000));
console.log(isNumeric(0.35));
console.log(isNumeric(-10.35));
console.log(isNumeric(2.534e25));
console.log(isNumeric('2.534e25'));
console.log(isNumeric('52334'));
console.log(isNumeric('-234'));
console.log(isNumeric(Infinity));
console.log(isNumeric(-Infinity));
console.log(isNumeric('Infinity'));
console.log(isNumeric('-Infinity'));

console.log('falses');
console.log(isNumeric(NaN));
console.log(isNumeric({}));
console.log(isNumeric([]));
console.log(isNumeric(''));
console.log(isNumeric('one'));
console.log(isNumeric(true));
console.log(isNumeric(false));
console.log(isNumeric());
console.log(isNumeric(undefined));
console.log(isNumeric(null));
console.log(isNumeric('-234aa'));

Note that it considers infinity a number.

Arrrgh! Don't listen to the regular expression answers. RegEx is icky for this, and I'm not talking just performance. It's so easy to make subtle, impossible to spot mistakes with your regular expression.

If you can't use isNaN(), this should work much better:

function IsNumeric(input)
{
    return (input - 0) == input && (''+input).trim().length > 0;
}

Here's how it works:

The (input - 0) expression forces JavaScript to do type coercion on your input value; it must first be interpreted as a number for the subtraction operation. If that conversion to a number fails, the expression will result in NaN. This numeric result is then compared to the original value you passed in. Since the left hand side is now numeric, type coercion is again used. Now that the input from both sides was coerced to the same type from the same original value, you would think they should always be the same (always true). However, there's a special rule that says NaN is never equal to NaN, and so a value that can't be converted to a number (and only values that cannot be converted to numbers) will result in false.

The check on the length is for a special case involving empty strings. Also note that it falls down on your 0x89f test, but that's because in many environments that's an okay way to define a number literal. If you want to catch that specific scenario you could add an additional check. Even better, if that's your reason for not using isNaN() then just wrap your own function around isNaN() that can also do the additional check.

In summary, if you want to know if a value can be converted to a number, actually try to convert it to a number.

I went back and did some research for why a whitespace string did not have the expected output, and I think I get it now: an empty string is coerced to 0 rather than NaN. Simply trimming the string before the length check will handle this case.

Running the unit tests against the new code and it only fails on the infinity and boolean literals, and the only time that should be a problem is if you're generating code (really, who would type in a literal and check if it's numeric? You should know), and that would be some strange code to generate.

But, again, the only reason ever to use this is if for some reason you have to avoid isNaN().

function isNumber(n) {
    return (n===n+''||n===n-0) && n*0==0 && /\S/.test(n);
}

Explanations:

(n===n-0||n===n+'') verifies if n is a number or a string (discards arrays, boolean, date, null, ...). You can replace (n===n-0||n===n+'') by n!==undefined && n!==null && (n.constructor===Number||n.constructor===String): significantly faster but less concise.

n*0==0 verifies if n is a finite number as isFinite(n) does. If you need to check strings that represent negative hexadecimal, just replace n*0==0 by something like n.toString().replace(/^\s*-/,'')*0==0.
It costs a little of course, so if you don't need it, don't use it.

/\S/.test(n) discards empty strings or strings, that contain only white-spaces (necessary since isFinite(n) or n*0==0 return a false positive in this case). You can reduce the number of call to .test(n) by using (n!=0||/0/.test(n)) instead of /\S/.test(n), or you can use a slightly faster but less concise test such as (n!=0||(n+'').indexOf('0')>=0): tiny improvement.

isNumeric=(el)=>{return Boolean(parseFloat(el)) && isFinite(el)}

Nothing very different but we can use Boolean constructor

Yeah, the built-in isNaN(object) will be much faster than any regex parsing, because it's built-in and compiled, instead of interpreted on the fly.

Although the results are somewhat different to what you're looking for (try it):

                                              // IS NUMERIC
document.write(!isNaN('-1') + "<br />");      // true
document.write(!isNaN('-1.5') + "<br />");    // true
document.write(!isNaN('0') + "<br />");       // true
document.write(!isNaN('0.42') + "<br />");    // true
document.write(!isNaN('.42') + "<br />");     // true
document.write(!isNaN('99,999') + "<br />");  // false
document.write(!isNaN('0x89f') + "<br />");   // true
document.write(!isNaN('#abcdef') + "<br />"); // false
document.write(!isNaN('1.2.3') + "<br />");   // false
document.write(!isNaN('') + "<br />");        // true
document.write(!isNaN('blah') + "<br />");    // false

To check if a variable contains a valid number and not just a String which looks like a number, Number.isFinite(value) can be used.

This is part of the language since ES2015

Examples:

Number.isFinite(Infinity)   // false
Number.isFinite(NaN)        // false
Number.isFinite(-Infinity)  // false

Number.isFinite(0)          // true
Number.isFinite(2e64)       // true

Number.isFinite('0')        // false
Number.isFinite(null)       // false

Only problem I had with @CMS's answer is the exclusion of NaN and Infinity, which are useful numbers for many situations. One way to check for NaN's is to check for numeric values that don't equal themselves, NaN != NaN! So there are really 3 tests you'd like to deal with ...

function isNumber(n) {
  n = parseFloat(n);
  return !isNaN(n) || n != n;
}
function isFiniteNumber(n) {
  n = parseFloat(n);
  return !isNaN(n) && isFinite(n);
}    
function isComparableNumber(n) {
  n = parseFloat(n);
  return (n >=0 || n < 0);
}

isFiniteNumber('NaN')
false
isFiniteNumber('OxFF')
true
isNumber('NaN')
true
isNumber(1/0-1/0)
true
isComparableNumber('NaN')
false
isComparableNumber('Infinity')
true

My isComparableNumber is pretty close to another elegant answer, but handles hex and other string representations of numbers.

This way seems to work well:

function IsNumeric(input){
    var RE = /^-{0,1}\d*\.{0,1}\d+$/;
    return (RE.test(input));
}

In one line:

const IsNumeric = (num) => /^-{0,1}\d*\.{0,1}\d+$/.test(num);

And to test it:

const IsNumeric = (num) => /^-{0,1}\d*\.{0,1}\d+$/.test(num);_x000D_
    _x000D_
    function TestIsNumeric(){_x000D_
        var results = ''_x000D_
        results += (IsNumeric('-1')?"Pass":"Fail") + ": IsNumeric('-1') => true\n";_x000D_
        results += (IsNumeric('-1.5')?"Pass":"Fail") + ": IsNumeric('-1.5') => true\n";_x000D_
        results += (IsNumeric('0')?"Pass":"Fail") + ": IsNumeric('0') => true\n";_x000D_
        results += (IsNumeric('0.42')?"Pass":"Fail") + ": IsNumeric('0.42') => true\n";_x000D_
        results += (IsNumeric('.42')?"Pass":"Fail") + ": IsNumeric('.42') => true\n";_x000D_
        results += (!IsNumeric('99,999')?"Pass":"Fail") + ": IsNumeric('99,999') => false\n";_x000D_
        results += (!IsNumeric('0x89f')?"Pass":"Fail") + ": IsNumeric('0x89f') => false\n";_x000D_
        results += (!IsNumeric('#abcdef')?"Pass":"Fail") + ": IsNumeric('#abcdef') => false\n";_x000D_
        results += (!IsNumeric('1.2.3')?"Pass":"Fail") + ": IsNumeric('1.2.3') => false\n";_x000D_
        results += (!IsNumeric('')?"Pass":"Fail") + ": IsNumeric('') => false\n";_x000D_
        results += (!IsNumeric('blah')?"Pass":"Fail") + ": IsNumeric('blah') => false\n";_x000D_
        _x000D_
        return results;_x000D_
    }_x000D_
_x000D_
console.log(TestIsNumeric());

.as-console-wrapper { max-height: 100% !important; top: 0; }

I borrowed that regex from http://www.codetoad.com/javascript/isnumeric.asp. Explanation:

/^ match beginning of string
-{0,1} optional negative sign
\d* optional digits
\.{0,1} optional decimal point
\d+ at least one digit
$/ match end of string

If I'm not mistaken, this should match any valid JavaScript number value, excluding constants (Infinity, NaN) and the sign operators +/- (because they are not actually part of the number as far as I concerned, they are separate operators):

I needed this for a tokenizer, where sending the number to JavaScript for evaluation wasn't an option... It's definitely not the shortest possible regular expression, but I believe it catches all the finer subtleties of JavaScript's number syntax.

/^(?:(?:(?:[1-9]\d*|\d)\.\d*|(?:[1-9]\d*|\d)?\.\d+|(?:[1-9]\d*|\d)) 
(?:[e]\d+)?|0[0-7]+|0x[0-9a-f]+)$/i

Valid numbers would include:

 - 0
 - 00
 - 01
 - 10
 - 0e1
 - 0e01
 - .0
 - 0.
 - .0e1
 - 0.e1
 - 0.e00
 - 0xf
 - 0Xf

Invalid numbers would be

 - 00e1
 - 01e1
 - 00.0
 - 00x0
 - .
 - .e0

To me, this is the best way:

isNumber : function(v){
   return typeof v === 'number' && isFinite(v);
}

The accepted answer failed your test #7 and I guess it's because you changed your mind. So this is a response to the accepted answer, with which I had issues.

During some projects I have needed to validate some data and be as certain as possible that it is a javascript numerical value that can be used in mathematical operations.

jQuery, and some other javascript libraries already include such a function, usually called isNumeric. There is also a post on stackoverflow that has been widely accepted as the answer, the same general routine that the afore mentioned libraries are using.

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

First, the code above would return true if the argument was an array of length 1, and that single element was of a type deemed as numeric by the above logic. In my opinion, if it's an array then its not numeric.

To alleviate this problem, I added a check to discount arrays from the logic

function isNumber(n) {
  return Object.prototype.toString.call(n) !== '[object Array]' &&!isNaN(parseFloat(n)) && isFinite(n);
}

Of course, you could also use Array.isArray, jquery $.isArray or prototype Object.isArray instead of Object.prototype.toString.call(n) !== '[object Array]'

My second issue was that Negative Hexadecimal integer literal strings ("-0xA" -> -10) were not being counted as numeric. However, Positive Hexadecimal integer literal strings ("0xA" -> 10) were treated as numeric. I needed both to be valid numeric.

I then modified the logic to take this into account.

function isNumber(n) {
  return Object.prototype.toString.call(n) !== '[object Array]' &&!isNaN(parseFloat(n)) && isFinite(n.toString().replace(/^-/, ''));
}

If you are worried about the creation of the regex each time the function is called then you could rewrite it within a closure, something like this

var isNumber = (function () {
  var rx = /^-/;

  return function (n) {
      return Object.prototype.toString.call(n) !== '[object Array]' &&!isNaN(parseFloat(n)) && isFinite(n.toString().replace(rx, ''));
  };
}());

I then took CMSs +30 test cases and cloned the testing on jsfiddle added my extra test cases and my above described solution.

It may not replace the widely accepted/used answer but if this is more of what you are expecting as results from your isNumeric function then hopefully this will be of some help.

EDIT: As pointed out by Bergi, there are other possible objects that could be considered numeric and it would be better to whitelist than blacklist. With this in mind I would add to the criteria.

I want my isNumeric function to consider only Numbers or Strings

With this in mind, it would be better to use

function isNumber(n) {
  return (Object.prototype.toString.call(n) === '[object Number]' || Object.prototype.toString.call(n) === '[object String]') &&!isNaN(parseFloat(n)) && isFinite(n.toString().replace(/^-/, ''));
}

Test the solutions

var testHelper = function() {_x000D_
_x000D_
  var testSuite = function() {_x000D_
    test("Integer Literals", function() {_x000D_
      ok(isNumber("-10"), "Negative integer string");_x000D_
      ok(isNumber("0"), "Zero string");_x000D_
      ok(isNumber("5"), "Positive integer string");_x000D_
      ok(isNumber(-16), "Negative integer number");_x000D_
      ok(isNumber(0), "Zero integer number");_x000D_
      ok(isNumber(32), "Positive integer number");_x000D_
      ok(isNumber("040"), "Octal integer literal string");_x000D_
      ok(isNumber(0144), "Octal integer literal");_x000D_
      ok(isNumber("-040"), "Negative Octal integer literal string");_x000D_
      ok(isNumber(-0144), "Negative Octal integer literal");_x000D_
      ok(isNumber("0xFF"), "Hexadecimal integer literal string");_x000D_
      ok(isNumber(0xFFF), "Hexadecimal integer literal");_x000D_
      ok(isNumber("-0xFF"), "Negative Hexadecimal integer literal string");_x000D_
      ok(isNumber(-0xFFF), "Negative Hexadecimal integer literal");_x000D_
    });_x000D_
_x000D_
    test("Foating-Point Literals", function() {_x000D_
      ok(isNumber("-1.6"), "Negative floating point string");_x000D_
      ok(isNumber("4.536"), "Positive floating point string");_x000D_
      ok(isNumber(-2.6), "Negative floating point number");_x000D_
      ok(isNumber(3.1415), "Positive floating point number");_x000D_
      ok(isNumber(8e5), "Exponential notation");_x000D_
      ok(isNumber("123e-2"), "Exponential notation string");_x000D_
    });_x000D_
_x000D_
    test("Non-Numeric values", function() {_x000D_
      equals(isNumber(""), false, "Empty string");_x000D_
      equals(isNumber("        "), false, "Whitespace characters string");_x000D_
      equals(isNumber("\t\t"), false, "Tab characters string");_x000D_
      equals(isNumber("abcdefghijklm1234567890"), false, "Alphanumeric character string");_x000D_
      equals(isNumber("xabcdefx"), false, "Non-numeric character string");_x000D_
      equals(isNumber(true), false, "Boolean true literal");_x000D_
      equals(isNumber(false), false, "Boolean false literal");_x000D_
      equals(isNumber("bcfed5.2"), false, "Number with preceding non-numeric characters");_x000D_
      equals(isNumber("7.2acdgs"), false, "Number with trailling non-numeric characters");_x000D_
      equals(isNumber(undefined), false, "Undefined value");_x000D_
      equals(isNumber(null), false, "Null value");_x000D_
      equals(isNumber(NaN), false, "NaN value");_x000D_
      equals(isNumber(Infinity), false, "Infinity primitive");_x000D_
      equals(isNumber(Number.POSITIVE_INFINITY), false, "Positive Infinity");_x000D_
      equals(isNumber(Number.NEGATIVE_INFINITY), false, "Negative Infinity");_x000D_
      equals(isNumber(new Date(2009, 1, 1)), false, "Date object");_x000D_
      equals(isNumber(new Object()), false, "Empty object");_x000D_
      equals(isNumber(function() {}), false, "Instance of a function");_x000D_
      equals(isNumber([]), false, "Empty Array");_x000D_
      equals(isNumber(["-10"]), false, "Array Negative integer string");_x000D_
      equals(isNumber(["0"]), false, "Array Zero string");_x000D_
      equals(isNumber(["5"]), false, "Array Positive integer string");_x000D_
      equals(isNumber([-16]), false, "Array Negative integer number");_x000D_
      equals(isNumber([0]), false, "Array Zero integer number");_x000D_
      equals(isNumber([32]), false, "Array Positive integer number");_x000D_
      equals(isNumber(["040"]), false, "Array Octal integer literal string");_x000D_
      equals(isNumber([0144]), false, "Array Octal integer literal");_x000D_
      equals(isNumber(["-040"]), false, "Array Negative Octal integer literal string");_x000D_
      equals(isNumber([-0144]), false, "Array Negative Octal integer literal");_x000D_
      equals(isNumber(["0xFF"]), false, "Array Hexadecimal integer literal string");_x000D_
      equals(isNumber([0xFFF]), false, "Array Hexadecimal integer literal");_x000D_
      equals(isNumber(["-0xFF"]), false, "Array Negative Hexadecimal integer literal string");_x000D_
      equals(isNumber([-0xFFF]), false, "Array Negative Hexadecimal integer literal");_x000D_
      equals(isNumber([1, 2]), false, "Array with more than 1 Positive interger number");_x000D_
      equals(isNumber([-1, -2]), false, "Array with more than 1 Negative interger number");_x000D_
    });_x000D_
  }_x000D_
_x000D_
  var functionsToTest = [_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(parseFloat(n)) && isFinite(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(n) && !isNaN(parseFloat(n));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN((n));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(parseFloat(n));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return typeof(n) != "boolean" && !isNaN(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return parseFloat(n) === Number(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return parseInt(n) === Number(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(Number(String(n)));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(+('' + n));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return (+n) == n;_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return n && /^-?\d+(\.\d+)?$/.test(n + '');_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return isFinite(Number(String(n)));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return isFinite(String(n));_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !isNaN(n) && !isNaN(parseFloat(n)) && isFinite(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return parseFloat(n) == n;_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return (n - 0) == n && n.length > 0;_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return typeof n === 'number' && isFinite(n);_x000D_
    },_x000D_
_x000D_
    function(n) {_x000D_
      return !Array.isArray(n) && !isNaN(parseFloat(n)) && isFinite(n.toString().replace(/^-/, ''));_x000D_
    }_x000D_
_x000D_
  ];_x000D_
_x000D_
_x000D_
  // Examines the functionsToTest array, extracts the return statement of each function_x000D_
  // and fills the toTest select element._x000D_
  var fillToTestSelect = function() {_x000D_
    for (var i = 0; i < functionsToTest.length; i++) {_x000D_
      var f = functionsToTest[i].toString();_x000D_
      var option = /[\s\S]*return ([\s\S]*);/.exec(f)[1];_x000D_
      $("#toTest").append('<option value="' + i + '">' + (i + 1) + '. ' + option + '</option>');_x000D_
    }_x000D_
  }_x000D_
_x000D_
  var performTest = function(functionNumber) {_x000D_
    reset(); // Reset previous test_x000D_
    $("#tests").html(""); //Clean test results_x000D_
    isNumber = functionsToTest[functionNumber]; // Override the isNumber global function with the one to test_x000D_
    testSuite(); // Run the test_x000D_
_x000D_
    // Get test results_x000D_
    var totalFail = 0;_x000D_
    var totalPass = 0;_x000D_
    $("b.fail").each(function() {_x000D_
      totalFail += Number($(this).html());_x000D_
    });_x000D_
    $("b.pass").each(function() {_x000D_
      totalPass += Number($(this).html());_x000D_
    });_x000D_
    $("#testresult").html(totalFail + " of " + (totalFail + totalPass) + " test failed.");_x000D_
_x000D_
    $("#banner").attr("class", "").addClass(totalFail > 0 ? "fail" : "pass");_x000D_
  }_x000D_
_x000D_
  return {_x000D_
    performTest: performTest,_x000D_
    fillToTestSelect: fillToTestSelect,_x000D_
    testSuite: testSuite_x000D_
  };_x000D_
}();_x000D_
_x000D_
_x000D_
$(document).ready(function() {_x000D_
  testHelper.fillToTestSelect();_x000D_
  testHelper.performTest(0);_x000D_
_x000D_
  $("#toTest").change(function() {_x000D_
    testHelper.performTest($(this).children(":selected").val());_x000D_
  });_x000D_
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js" type="text/javascript"></script>_x000D_
<script src="https://rawgit.com/Xotic750/testrunner-old/master/testrunner.js" type="text/javascript"></script>_x000D_
<link href="https://rawgit.com/Xotic750/testrunner-old/master/testrunner.css" rel="stylesheet" type="text/css">_x000D_
<h1>isNumber Test Cases</h1>_x000D_
_x000D_
<h2 id="banner" class="pass"></h2>_x000D_
_x000D_
<h2 id="userAgent">Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11</h2>_x000D_
_x000D_
<div id="currentFunction"></div>_x000D_
_x000D_
<div id="selectFunction">_x000D_
  <label for="toTest" style="font-weight:bold; font-size:Large;">Select function to test:</label>_x000D_
  <select id="toTest" name="toTest">_x000D_
  </select>_x000D_
</div>_x000D_
_x000D_
<div id="testCode"></div>_x000D_
_x000D_
<ol id="tests">_x000D_
  <li class="pass">_x000D_
    <strong>Integer Literals <b style="color:black;">(0, 10, 10)</b></strong>_x000D_
_x000D_
    <ol style="display: none;">_x000D_
      <li class="pass">Negative integer string</li>_x000D_
_x000D_
      <li class="pass">Zero string</li>_x000D_
_x000D_
      <li class="pass">Positive integer string</li>_x000D_
_x000D_
      <li class="pass">Negative integer number</li>_x000D_
_x000D_
      <li class="pass">Zero integer number</li>_x000D_
_x000D_
      <li class="pass">Positive integer number</li>_x000D_
_x000D_
      <li class="pass">Octal integer literal string</li>_x000D_
_x000D_
      <li class="pass">Octal integer literal</li>_x000D_
_x000D_
      <li class="pass">Hexadecimal integer literal string</li>_x000D_
_x000D_
      <li class="pass">Hexadecimal integer literal</li>_x000D_
    </ol>_x000D_
  </li>_x000D_
_x000D_
  <li class="pass">_x000D_
    <strong>Foating-Point Literals <b style="color:black;">(0, 6, 6)</b></strong>_x000D_
_x000D_
    <ol style="display: none;">_x000D_
      <li class="pass">Negative floating point string</li>_x000D_
_x000D_
      <li class="pass">Positive floating point string</li>_x000D_
_x000D_
      <li class="pass">Negative floating point number</li>_x000D_
_x000D_
      <li class="pass">Positive floating point number</li>_x000D_
_x000D_
      <li class="pass">Exponential notation</li>_x000D_
_x000D_
      <li class="pass">Exponential notation string</li>_x000D_
    </ol>_x000D_
  </li>_x000D_
_x000D_
  <li class="pass">_x000D_
    <strong>Non-Numeric values <b style="color:black;">(0, 18, 18)</b></strong>_x000D_
_x000D_
    <ol style="display: none;">_x000D_
      <li class="pass">Empty string: false</li>_x000D_
_x000D_
      <li class="pass">Whitespace characters string: false</li>_x000D_
_x000D_
      <li class="pass">Tab characters string: false</li>_x000D_
_x000D_
      <li class="pass">Alphanumeric character string: false</li>_x000D_
_x000D_
      <li class="pass">Non-numeric character string: false</li>_x000D_
_x000D_
      <li class="pass">Boolean true literal: false</li>_x000D_
_x000D_
      <li class="pass">Boolean false literal: false</li>_x000D_
_x000D_
      <li class="pass">Number with preceding non-numeric characters: false</li>_x000D_
_x000D_
      <li class="pass">Number with trailling non-numeric characters: false</li>_x000D_
_x000D_
      <li class="pass">Undefined value: false</li>_x000D_
_x000D_
      <li class="pass">Null value: false</li>_x000D_
_x000D_
      <li class="pass">NaN value: false</li>_x000D_
_x000D_
      <li class="pass">Infinity primitive: false</li>_x000D_
_x000D_
      <li class="pass">Positive Infinity: false</li>_x000D_
_x000D_
      <li class="pass">Negative Infinity: false</li>_x000D_
_x000D_
      <li class="pass">Date object: false</li>_x000D_
_x000D_
      <li class="pass">Empty object: false</li>_x000D_
_x000D_
      <li class="pass">Instance of a function: false</li>_x000D_
    </ol>_x000D_
  </li>_x000D_
</ol>_x000D_
_x000D_
<div id="main">_x000D_
  This page contains tests for a set of isNumber functions. To see them, take a look at the source._x000D_
</div>_x000D_
_x000D_
<div>_x000D_
  <p class="result">Tests completed in 0 milliseconds._x000D_
    <br>0 tests of 0 failed.</p>_x000D_
</div>

Best way to do this is like this:

function isThisActuallyANumber(data){
    return ( typeof data === "number" && !isNaN(data) );
}

I use this way to chack that varible is numeric:

v * 1 == v

A couple of tests to add:

IsNumeric('01.05') => false
IsNumeric('1.') => false
IsNumeric('.') => false

I came up with this:

function IsNumeric(input) {
    return /^-?(0|[1-9]\d*|(?=\.))(\.\d+)?$/.test(input);
}

The solution covers:

• An optional negative sign at the beginning
• A single zero, or one or more digits not starting with 0, or nothing so long as a period follows
• A period that is followed by 1 or more numbers

I realize the original question did not mention jQuery, but if you do use jQuery, you can do:

$.isNumeric(val)

Simple.

https://api.jquery.com/jQuery.isNumeric/ (as of jQuery 1.7)