Validate decimal numbers in JavaScript - IsNumeric()

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().

This way seems to work well:

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

And to test it:

// alert(TestIsNumeric());

function TestIsNumeric(){
    var results = ''
    results += (IsNumeric('-1')?"Pass":"Fail") + ": IsNumeric('-1') => true\n";
    results += (IsNumeric('-1.5')?"Pass":"Fail") + ": IsNumeric('-1.5') => true\n";
    results += (IsNumeric('0')?"Pass":"Fail") + ": IsNumeric('0') => true\n";
    results += (IsNumeric('0.42')?"Pass":"Fail") + ": IsNumeric('0.42') => true\n";
    results += (IsNumeric('.42')?"Pass":"Fail") + ": IsNumeric('.42') => true\n";
    results += (!IsNumeric('99,999')?"Pass":"Fail") + ": IsNumeric('99,999') => false\n";
    results += (!IsNumeric('0x89f')?"Pass":"Fail") + ": IsNumeric('0x89f') => false\n";
    results += (!IsNumeric('#abcdef')?"Pass":"Fail") + ": IsNumeric('#abcdef') => false\n";
    results += (!IsNumeric('1.2.3')?"Pass":"Fail") + ": IsNumeric('1.2.3') => false\n";
    results += (!IsNumeric('')?"Pass":"Fail") + ": IsNumeric('') => false\n";
    results += (!IsNumeric('blah')?"Pass":"Fail") + ": IsNumeric('blah') => false\n";

    return results;
}

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

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

This works for 0x23 type numbers as well.

Yahoo! UI uses this:

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

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() {

  var testSuite = function() {
    test("Integer Literals", function() {
      ok(isNumber("-10"), "Negative integer string");
      ok(isNumber("0"), "Zero string");
      ok(isNumber("5"), "Positive integer string");
      ok(isNumber(-16), "Negative integer number");
      ok(isNumber(0), "Zero integer number");
      ok(isNumber(32), "Positive integer number");
      ok(isNumber("040"), "Octal integer literal string");
      ok(isNumber(0144), "Octal integer literal");
      ok(isNumber("-040"), "Negative Octal integer literal string");
      ok(isNumber(-0144), "Negative Octal integer literal");
      ok(isNumber("0xFF"), "Hexadecimal integer literal string");
      ok(isNumber(0xFFF), "Hexadecimal integer literal");
      ok(isNumber("-0xFF"), "Negative Hexadecimal integer literal string");
      ok(isNumber(-0xFFF), "Negative Hexadecimal integer literal");
    });

    test("Foating-Point Literals", function() {
      ok(isNumber("-1.6"), "Negative floating point string");
      ok(isNumber("4.536"), "Positive floating point string");
      ok(isNumber(-2.6), "Negative floating point number");
      ok(isNumber(3.1415), "Positive floating point number");
      ok(isNumber(8e5), "Exponential notation");
      ok(isNumber("123e-2"), "Exponential notation string");
    });

    test("Non-Numeric values", function() {
      equals(isNumber(""), false, "Empty string");
      equals(isNumber("        "), false, "Whitespace characters string");
      equals(isNumber("\t\t"), false, "Tab characters string");
      equals(isNumber("abcdefghijklm1234567890"), false, "Alphanumeric character string");
      equals(isNumber("xabcdefx"), false, "Non-numeric character string");
      equals(isNumber(true), false, "Boolean true literal");
      equals(isNumber(false), false, "Boolean false literal");
      equals(isNumber("bcfed5.2"), false, "Number with preceding non-numeric characters");
      equals(isNumber("7.2acdgs"), false, "Number with trailling non-numeric characters");
      equals(isNumber(undefined), false, "Undefined value");
      equals(isNumber(null), false, "Null value");
      equals(isNumber(NaN), false, "NaN value");
      equals(isNumber(Infinity), false, "Infinity primitive");
      equals(isNumber(Number.POSITIVE_INFINITY), false, "Positive Infinity");
      equals(isNumber(Number.NEGATIVE_INFINITY), false, "Negative Infinity");
      equals(isNumber(new Date(2009, 1, 1)), false, "Date object");
      equals(isNumber(new Object()), false, "Empty object");
      equals(isNumber(function() {}), false, "Instance of a function");
      equals(isNumber([]), false, "Empty Array");
      equals(isNumber(["-10"]), false, "Array Negative integer string");
      equals(isNumber(["0"]), false, "Array Zero string");
      equals(isNumber(["5"]), false, "Array Positive integer string");
      equals(isNumber([-16]), false, "Array Negative integer number");
      equals(isNumber([0]), false, "Array Zero integer number");
      equals(isNumber([32]), false, "Array Positive integer number");
      equals(isNumber(["040"]), false, "Array Octal integer literal string");
      equals(isNumber([0144]), false, "Array Octal integer literal");
      equals(isNumber(["-040"]), false, "Array Negative Octal integer literal string");
      equals(isNumber([-0144]), false, "Array Negative Octal integer literal");
      equals(isNumber(["0xFF"]), false, "Array Hexadecimal integer literal string");
      equals(isNumber([0xFFF]), false, "Array Hexadecimal integer literal");
      equals(isNumber(["-0xFF"]), false, "Array Negative Hexadecimal integer literal string");
      equals(isNumber([-0xFFF]), false, "Array Negative Hexadecimal integer literal");
      equals(isNumber([1, 2]), false, "Array with more than 1 Positive interger number");
      equals(isNumber([-1, -2]), false, "Array with more than 1 Negative interger number");
    });
  }

  var functionsToTest = [

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

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

    function(n) {
      return !isNaN((n));
    },

    function(n) {
      return !isNaN(parseFloat(n));
    },

    function(n) {
      return typeof(n) != "boolean" && !isNaN(n);
    },

    function(n) {
      return parseFloat(n) === Number(n);
    },

    function(n) {
      return parseInt(n) === Number(n);
    },

    function(n) {
      return !isNaN(Number(String(n)));
    },

    function(n) {
      return !isNaN(+('' + n));
    },

    function(n) {
      return (+n) == n;
    },

    function(n) {
      return n && /^-?\d+(\.\d+)?$/.test(n + '');
    },

    function(n) {
      return isFinite(Number(String(n)));
    },

    function(n) {
      return isFinite(String(n));
    },

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

    function(n) {
      return parseFloat(n) == n;
    },

    function(n) {
      return (n - 0) == n && n.length > 0;
    },

    function(n) {
      return typeof n === 'number' && isFinite(n);
    },

    function(n) {
      return !Array.isArray(n) && !isNaN(parseFloat(n)) && isFinite(n.toString().replace(/^-/, ''));
    }

  ];


  // Examines the functionsToTest array, extracts the return statement of each function
  // and fills the toTest select element.
  var fillToTestSelect = function() {
    for (var i = 0; i < functionsToTest.length; i++) {
      var f = functionsToTest[i].toString();
      var option = /[\s\S]*return ([\s\S]*);/.exec(f)[1];
      $("#toTest").append('<option value="' + i + '">' + (i + 1) + '. ' + option + '</option>');
    }
  }

  var performTest = function(functionNumber) {
    reset(); // Reset previous test
    $("#tests").html(""); //Clean test results
    isNumber = functionsToTest[functionNumber]; // Override the isNumber global function with the one to test
    testSuite(); // Run the test

    // Get test results
    var totalFail = 0;
    var totalPass = 0;
    $("b.fail").each(function() {
      totalFail += Number($(this).html());
    });
    $("b.pass").each(function() {
      totalPass += Number($(this).html());
    });
    $("#testresult").html(totalFail + " of " + (totalFail + totalPass) + " test failed.");

    $("#banner").attr("class", "").addClass(totalFail > 0 ? "fail" : "pass");
  }

  return {
    performTest: performTest,
    fillToTestSelect: fillToTestSelect,
    testSuite: testSuite
  };
}();


$(document).ready(function() {
  testHelper.fillToTestSelect();
  testHelper.performTest(0);

  $("#toTest").change(function() {
    testHelper.performTest($(this).children(":selected").val());
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js" type="text/javascript"></script>
<script src="http://dl.getdropbox.com/u/35146/js/tests/testrunner.js" type="text/javascript"></script>
<link href="http://dl.getdropbox.com/u/35146/js/tests/testsuite.css" rel="stylesheet" type="text/css">
<h1>isNumber Test Cases</h1>

<h2 id="banner" class="pass"></h2>

<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>

<div id="currentFunction"></div>

<div id="selectFunction">
  <label for="toTest" style="font-weight:bold; font-size:Large;">Select function to test:</label>
  <select id="toTest" name="toTest">
    <option value="0">
      1. !isNaN(parseFloat(n)) &amp;&amp; isFinite(n)
    </option>

    <option value="1">
      2. !isNaN(n) &amp;&amp; !isNaN(parseFloat(n))
    </option>

    <option value="2">
      3. !isNaN((n))
    </option>

    <option value="3">
      4. !isNaN(parseFloat(n))
    </option>

    <option value="4">
      5. typeof(n) != "boolean" &amp;&amp; !isNaN(n)
    </option>

    <option value="5">
      6. parseFloat(n) === Number(n)
    </option>

    <option value="6">
      7. parseInt(n) === Number(n)
    </option>

    <option value="7">
      8. !isNaN(Number(String(n)))
    </option>

    <option value="8">
      9. !isNaN(+('' + n))
    </option>

    <option value="9">
      10. (+n) == n
    </option>

    <option value="10">
      11. n &amp;&amp; /^-?\d+(\.\d+)?$/.test(n + '')
    </option>

    <option value="11">
      12. isFinite(Number(String(n)))
    </option>

    <option value="12">
      13. isFinite(String(n))
    </option>

    <option value="13">
      14. !isNaN(n) &amp;&amp; !isNaN(parseFloat(n)) &amp;&amp; isFinite(n)
    </option>

    <option value="14">
      15. parseFloat(n) == n
    </option>

    <option value="15">
      16. (n - 0) == n &amp;&amp; n.length &gt; 0
    </option>

    <option value="16">
      17. typeof n === 'number' &amp;&amp; isFinite(n)
    </option>

    <option value="17">
      18. !Array.isArray(n) &amp;&amp; !isNaN(parseFloat(n)) &amp;&amp; isFinite(n.toString().replace(/^-/, ''))
    </option>
  </select>
</div>

<div id="testCode"></div>

<ol id="tests">
  <li class="pass">
    <strong>Integer Literals <b style="color:black;">(0, 10, 10)</b></strong>

    <ol style="display: none;">
      <li class="pass">Negative integer string</li>

      <li class="pass">Zero string</li>

      <li class="pass">Positive integer string</li>

      <li class="pass">Negative integer number</li>

      <li class="pass">Zero integer number</li>

      <li class="pass">Positive integer number</li>

      <li class="pass">Octal integer literal string</li>

      <li class="pass">Octal integer literal</li>

      <li class="pass">Hexadecimal integer literal string</li>

      <li class="pass">Hexadecimal integer literal</li>
    </ol>
  </li>

  <li class="pass">
    <strong>Foating-Point Literals <b style="color:black;">(0, 6, 6)</b></strong>

    <ol style="display: none;">
      <li class="pass">Negative floating point string</li>

      <li class="pass">Positive floating point string</li>

      <li class="pass">Negative floating point number</li>

      <li class="pass">Positive floating point number</li>

      <li class="pass">Exponential notation</li>

      <li class="pass">Exponential notation string</li>
    </ol>
  </li>

  <li class="pass">
    <strong>Non-Numeric values <b style="color:black;">(0, 18, 18)</b></strong>

    <ol style="display: none;">
      <li class="pass">Empty string: false</li>

      <li class="pass">Whitespace characters string: false</li>

      <li class="pass">Tab characters string: false</li>

      <li class="pass">Alphanumeric character string: false</li>

      <li class="pass">Non-numeric character string: false</li>

      <li class="pass">Boolean true literal: false</li>

      <li class="pass">Boolean false literal: false</li>

      <li class="pass">Number with preceding non-numeric characters: false</li>

      <li class="pass">Number with trailling non-numeric characters: false</li>

      <li class="pass">Undefined value: false</li>

      <li class="pass">Null value: false</li>

      <li class="pass">NaN value: false</li>

      <li class="pass">Infinity primitive: false</li>

      <li class="pass">Positive Infinity: false</li>

      <li class="pass">Negative Infinity: false</li>

      <li class="pass">Date object: false</li>

      <li class="pass">Empty object: false</li>

      <li class="pass">Instance of a function: false</li>
    </ol>
  </li>
</ol>

<div id="main">
  This page contains tests for a set of isNumber functions. To see them, take a look at the source.
</div>

<div>
  <p class="result">Tests completed in 0 milliseconds.
    <br>0 tests of 0 failed.</p>
</div>

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

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

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)

It can be done without RegExp as

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

To me, this is the best way:

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

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.

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

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!

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.

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.

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)

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.

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.

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));
}

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'm using simpler solution:

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

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

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

@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.

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): http://stackoverflow.com/a/1561597/1985601

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.

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

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

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.

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.