Check whether variable is number or string in JavaScript

Question

Does anyone know how can I check whether a variable is a number or a string in JavaScript

User · Answer

the best way i found which also thinks of positive and negative numbers is from : O'Reilly Javascript and DHTML Cookbook :

function isNumber(elem) {
var str = elem.value;
var oneDecimal = false;
var oneChar = 0;
// make sure value hasn't cast to a number data type
str = str.toString( );
for (var i = 0; i < str.length; i++) {
    oneChar = str.charAt(i).charCodeAt(0);
    // OK for minus sign as first character
    if (oneChar =  = 45) {
        if (i =  = 0) {
            continue;
        } else {
            alert("Only the first character may be a minus sign.");
            return false;
        }
    }
    // OK for one decimal point
    if (oneChar =  = 46) {
        if (!oneDecimal) {
            oneDecimal = true;
            continue;
        } else {
            alert("Only one decimal is allowed in a number.");
            return false;
        }
    }
    // characters outside of 0 through 9 not OK
    if (oneChar < 48 || oneChar > 57) {
        alert("Enter only numbers into the field.");
        return false;
    }
}
return true;

}

User · Answer

You re looking for isNaN      x000D   x000D  console log  isNaN 123    x000D  console log  isNaN -1 23    x000D  console log  isNaN 5-2    x000D  console log  isNaN 0    x000D  console log  isNaN  0     x000D  console log  isNaN  2     x000D  console log  isNaN  Hello     x000D  console log  isNaN  2005 12 12     x000D   x000D   x000D    See JavaScript isNaN   Function at MDN

User · Answer

uh  how about just   function IsString obj        return obj     undefined  amp  amp  obj    null  amp  amp  obj toLowerCase     undefined      After further review many months later  this only guarantees obj is an object that has the method or property name toLowerCase defined   I am ashamed of my answer   Please see top-voted typeof one

User · Answer

Try this    lt script gt  var regInteger     -  d      function isInteger  str             return regInteger test  str       if isInteger  1a11         console log   Integer       else      console log   Non Integer        lt  script gt

User · Answer

What do you thing about this one    const numberOrString  10   const isNumber    isNaN numberOrString 1

User · Answer

since a string as  1234  with typeof will show  string   and the inverse cannot ever happen  typeof 123 will always be number   the best is to use a simple regex    -  d    test var   Or a more advanced to match floats  integers and negative numbers      -      d       d      The important side of  test is that it WON T throw an exception if the var isn t an string  the value can be anything      var val  regex       -      d       d        regex test val           false  val    1234   regex test val           true val    -213   regex test val           true val    -213 2312   regex test val           true val     213 2312   regex test val           true val   123  regex test val           true val   new Number 123   regex test val           true val   new String  123    regex test val           true val    1234e   regex test val           false  val       regex test val           false  val   false  regex test val           false  regex test undefined     false  regex test null          false  regex test window        false  regex test document      false    If you are looking for the real type  then typeof alone will do

User · Answer

Type checking  You can check the type of variable by using typeof operator   typeof variable   Value checking  The code below returns true for numbers and false for anything else    isNaN  variable

User · Answer

Beware that typeof NaN is     number   typeof NaN      number      true

User · Answer

If you re dealing with literal notation  and not constructors  you can use typeof    typeof  Hello World      string typeof 123               number   If you re creating numbers and strings via a constructor  such as var foo   new String  foo    you should keep in mind that typeof may return object for foo    Perhaps a more foolproof method of checking the type would be to utilize the method found in underscore js  annotated source can be found here    var toString   Object prototype toString     isString   function  obj      return toString call obj       object String        This returns a boolean true for the following     isString  Jonathan       true   isString new String  Jonathan        true

User · Answer

testing data types accurately in JavaScript  opposed to  typeof     from http   bonsaiden github com JavaScript-Garden  function is type  obj        var clas   Object prototype toString call obj  slice 8  -1       return obj     undefined  amp  amp  obj     null  amp  amp  clas     type       basic usage is  String    test       true is  Array   true      false   Or adapt it to return an unknown type   function realTypeOf obj        return Object prototype toString call obj  slice 8  -1        usage realTypeOf 999       Number    May 12  2012 Update  Full example at Javascript  A Better typeof

User · Answer

Check if the value is a string literal or String object   function isString o        return typeof o     string      typeof o     object   amp  amp  o constructor     String       Unit test   function assertTrue value  message        if   value            alert  Assertion error      message            function assertFalse value  message        assertTrue  value  message      assertTrue isString  string literal     number literal    assertTrue isString new String  String object      String object    assertFalse isString 1    number literal    assertFalse isString true    boolean literal    assertFalse isString       object      Checking for a number is similar   function isNumber o        return typeof o     number      typeof o     object   amp  amp  o constructor     Number

User · Answer

The best way I have found is to either check for a method on the string  i e    if  x substring       do string thing   else     do other thing     or if you want to do something with the number check for a number property   if  x toFixed       do number thing   else      do other thing     This is sort of like  duck typing   it s up to you which way makes the most sense  I don t have enough karma to comment  but typeof fails for boxed strings and numbers  i e    alert typeof new String  Hello World     alert typeof new Number 5      will alert  object

User · Answer

Errr  Just use regular expressions      function isInteger val      return val match    0-9        function isFloat val      return val match    0-9      0-9

User · Answer

function IsNumeric num        return   num  gt  0    num  lt  0  amp  amp   parseInt num   num

User · Answer

Since ES2015 the correct way to check if a variable holds a valid number is Number isFinite value   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

User · Answer

typeof works very well for me in most case  You can try using an if statement  if typeof x      string     typeof x      number         console log  Your statement        where x is any variable name of your choice

User · Answer

Simple and thorough   function isNumber x      return parseFloat x     x      Test cases   console log     TRUE CASES       console log isNumber 0    console log isNumber -1    console log isNumber -500    console log isNumber 15000    console log isNumber 0 35    console log isNumber -10 35    console log isNumber 2 534e25    console log isNumber  2 534e25     console log isNumber  52334     console log isNumber  -234     console log isNumber Infinity    console log isNumber -Infinity    console log isNumber  Infinity     console log isNumber  -Infinity      console log     FALSE CASES       console log isNumber NaN    console log isNumber       console log isNumber       console log isNumber       console log isNumber  one     console log isNumber true    console log isNumber false    console log isNumber     console log isNumber undefined    console log isNumber null    console log isNumber  -234aa

User · Answer

This solution resolves many of the issues raised here   This is by far the most reliable method I have used by far  I did not invent this  and cannot recall where I originally found it   But it works where other techniques fail      Begin public utility  getVarType     Returns  Function    Object    Array       String    Number    Boolean   or  Undefined  getVarType   function   data      if  undefined     data    return  Undefined       if  data     null    return  Null       return    toString call data  slice 8  -1           End public utility  getVarType    Example of correctness  var str   new String    console warn  getVarType str        Reports  String      console warn  typeof str            Reports  object   var num   new Number    console warn  getVarType num        Reports  Number  console warn  typeof num            Reports  object   var list       console warn  getVarType  list         Reports  Array  console warn  typeof list              Reports  object

User · Answer

Here s an approach based on the idea of coercing the input to a number or string by adding zero or the null string  and then do a typed equality comparison   function is number x    return x     x 0     function is string x    return x     x         For some unfathomable reason  x   x 0 seems to perform better than x    x   Are there any cases where this fails   In the same vein   function is boolean x    return x       x      This appears to be mildly faster than either x   true    x   false or typeof x    boolean   and much faster than x   Boolean x     Then there s also   function is regexp x     return x     RegExp x       All these depend on the existence of an  identity  operation particular to each type which can be applied to any value and reliably produce a value of the type in question  I cannot think of such an operation for dates   For NaN  there is  function is nan x    return x     x     This is basically underscore s version  and as it stands is about four times faster than isNaN    but the comments in the underscore source mention that  NaN is the only number that does not equal itself  and adds a check for   isNumber  Why  What other objects would not equal themselves  Also  underscore uses x      x--but what difference could the   here make   Then for the paranoid   function is undefined x    return x      0       or this   function is undefined x    return x   void 0

User · Answer

BitOfUniverse s answer is good  and I come up with a new way   function isNum n        return  isNaN n 0      isNum         false isNum 2       true isNum  2k      false isNum  2      true   I know 0 can t be dividend  but here the function works perfectly

User · Answer

XOR operation can be used to detect number or string  number   0 will always give the number as output and string   0 will give 0 as output   Example      1   2   0   2    2    2    0    2    3    Str    0   0

User · Answer

For detecting numbers  the following passage from JavaScript  The Good Parts by Douglas Crockford is relevant      The isFinite function is the best way of determining whether a value can be used as a number because it rejects NaN and Infinity   Unfortunately  isFinite will attempt to convert its operand to a number  so it is not a good test if a value is not actually a number  You may want to define your own isNumber function    var isNumber   function isNumber value    return typeof value      number   amp  amp              isFinite value

User · Answer

I think converting the var to a string decreases the performance  at least this test performed in the latest browsers shows so   So if you care about performance  I would  I d use this   typeof str      string     str instanceof String   for checking if the variable is a string  even if you use var str   new String  foo    str instanceof String would return true    As for checking if it s a number I would go for the native  isNaN  function

User · Answer

Can you just divide it by 1   I assume the issue would be a string input like   123ABG   var Check    123ABG   if Check    Check   1    alert  This IS a number  n      else   alert  This is NOT a number  n       Just a way I did it recently

User · Answer

Best way to do this   function isNumber num      return  typeof num     string     typeof num     number    amp  amp   isNaN num - 0   amp  amp  num              This satisfies the following test cases   assertEquals  ISNUMBER-True  0   true  isNumber 0    assertEquals  ISNUMBER-True  1   true  isNumber -1    assertEquals  ISNUMBER-True  2   true  isNumber -500    assertEquals  ISNUMBER-True  3   true  isNumber 15000    assertEquals  ISNUMBER-True  4   true  isNumber 0 35    assertEquals  ISNUMBER-True  5   true  isNumber -10 35    assertEquals  ISNUMBER-True  6   true  isNumber 2 534e25    assertEquals  ISNUMBER-True  7   true  isNumber  2 534e25     assertEquals  ISNUMBER-True  8   true  isNumber  52334     assertEquals  ISNUMBER-True  9   true  isNumber  -234      assertEquals  ISNUMBER-False  0   false  isNumber NaN    assertEquals  ISNUMBER-False  1   false  isNumber       assertEquals  ISNUMBER-False  2   false  isNumber       assertEquals  ISNUMBER-False  3   false  isNumber       assertEquals  ISNUMBER-False  4   false  isNumber  one     assertEquals  ISNUMBER-False  5   false  isNumber true    assertEquals  ISNUMBER-False  6   false  isNumber false    assertEquals  ISNUMBER-False  7   false  isNumber     assertEquals  ISNUMBER-False  8   false  isNumber undefined    assertEquals  ISNUMBER-False  9   false  isNumber null

User · Answer

Very late to the party  however  the following has always worked well for me when I want to check whether some input is either a string or a number in one shot   return   Object prototype toString call input  match    object  String Number

User · Answer

Created a jsperf on the checking if a variable is a number  Quite interesting  typeof actually has a performance use  Using typeof for anything other than numbers  generally goes a 1 3rd the speed as a variable constructor since the majority of data types in javascript are Objects  numbers are not   http   jsperf com jemiloii-fastest-method-to-check-if-type-is-a-number  typeof variable      number   fastest   if you want a number  such as 5  and not  5  typeof parseFloat variable       number   fastest   if you want a number  such as 5  and  5   isNaN   is slower  but not that much slower  I had high hopes for parseInt and parseFloat  however they were horribly slower

User · Answer

jQuery uses this   function isNumber obj      return  isNaN  parseFloat  obj      amp  amp  isFinite  obj

User · Answer

Or just use the invert of isNaN     if  isNaN data     do something with the number else   it is a string   And yes  using jQuery s   isNumeric   is more fun for the buck

User · Answer

Simply use   myVar constructor    String   or  myVar constructor    Number   if you want to handle strings defined as objects or literals and saves you don t want to use a  helper function

User · Answer

Best way to do that is using isNaN   type casting   Updated all-in method   function isNumber n    return  isNaN parseFloat n    amp  amp   isNaN n - 0      The same using regex   function isNumber n    return   -   d      e-  d      test n       ------------------------  isNumber  123       true   isNumber  123abc       false   isNumber 5      true   isNumber  q345       false isNumber null      false isNumber undefined      false isNumber false      false isNumber            false

User · Answer

Jsut an FYI  if you re using jQuery you have    isNumeric      to handle this  More details on http   api jquery com jQuery isNumeric

[javascript] Check whether variable is number or string in JavaScript

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