How to check if a variable is an integer in JavaScript

Question

How do I check if a variable is an integer in JavaScript  and throw an alert if it isn t   I tried this  but it doesn t work    lt html gt       lt head gt           lt script type  text javascript  gt              var data   22              alert NaN data             lt  script gt       lt  head gt   lt  html gt

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Be careful while using     num   1   empty string      or boolean  true or false  will return as integer  You might not want to do that  false   1    true      1   true   Number isInteger data   Number isInteger 22     true Number isInteger 22 2     false Number isInteger  22      false   build in function in the browser  Dosnt support older browsers  Alternatives   Math round num     num   However  Math round   also will fail for empty string and boolean

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Lodash https   lodash com docs isInteger  since 4 0 0  has function to check if variable is an integer     isInteger 3        true    isInteger Number MIN VALUE        false    isInteger Infinity        false    isInteger  3         false

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You can use a simple regular expression   function isInt value        var er     -  0-9          return er test value

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What about large integers  bigint   Most of these answers fail on large integers  253 and larger   Bitwise tests e g   x   0      x   testing typeof x      number   regular int functions  e g  parseInt   regular arithmetics fail on large integers  This can be resolved by using BigInt  I ve compiled several answers into one snippet to show the results  Most outright fail with large integers  while others work  except when passed the type BigInt  e g  1n   I ve not included duplicate answers and have also left out any answers that allow decimals or don t attempt to test type   x000D   x000D     these all fail n   1000000000000000000000000000000 b   1n     These all fail on large integers   https   stackoverflow com a 14636652 3600709 console log  fail  1 n     parseInt n  10     https   stackoverflow com a 14794066 3600709 console log  fail  2  isNaN n   amp  amp  parseInt Number n      n  amp  amp   isNaN parseInt n  10    console log  fail  2  isNaN n   amp  amp   parseFloat n    0      parseFloat n   console log  fail  2  isNaN n   amp  amp   function x    return  x   0      x     parseFloat n      https   stackoverflow com a 21742529 3600709 console log  fail  3 n      n    https   stackoverflow com a 28211631 3600709 console log  fail  4  isNaN n   amp  amp  parseInt n     parseFloat n     https   stackoverflow com a 41854178 3600709 console log  fail  5 String parseInt n  10       String n       These ones work for integers  but not BigInt types  e g  1n    https   stackoverflow com a 14636725 3600709 console log  partial  1 typeof n    number   amp  amp   n 1    0     this one works console log  partial  1 typeof b    number   amp  amp   b 1    0     this one fails   https   stackoverflow com a 27424770 3600709 console log  partial  2 Number isInteger n      this one works console log  partial  2 Number isInteger b      this one fails   https   stackoverflow com a 14636638 3600709 console log  partial  3 n   1     0  console log  partial  3 b   1     0     gives uncaught type on BigInt x000D   x000D   x000D   Checking type If you actually want to test the incoming value s type to ensure it s an integer  use this instead  function isInt value        try           BigInt value          return    string   object   boolean   includes typeof value        catch e            return false           x000D   x000D  function isInt value        try           BigInt value          return    string   object   boolean   includes typeof value        catch e            return false          console log  --- should be false   console log isInt undefined   console log isInt      console log isInt null   console log isInt      console log isInt      console log isInt 1 1e-1   console log isInt 1 1   console log isInt true   console log isInt NaN   console log isInt  1    console log isInt function       console log isInt Infinity    console log  --- should be true   console log isInt 10   console log isInt 0x11   console log isInt 0   console log isInt -10000   console log isInt 100000000000000000000000000000000000000   console log isInt 1n   x000D   x000D   x000D    Without checking type If you don t care if the incoming type is actually boolean  string  etc  converted into a number  then just use the following  function isInt value        try           BigInt value          return true       catch e            return false           x000D   x000D  function isInt value        try           BigInt value          return true       catch e            return false          console log  --- should be false   console log isInt undefined   console log isInt null   console log isInt      console log isInt 1 1e-1   console log isInt 1 1   console log isInt NaN   console log isInt function       console log isInt Infinity    console log  --- should be true   console log isInt 10   console log isInt 0x11   console log isInt 0   console log isInt -10000   console log isInt 100000000000000000000000000000000000000   console log isInt 1n      gets converted to number console log isInt      console log isInt      console log isInt true   console log isInt  1    x000D   x000D   x000D

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I had to check if a variable  string or number  is an integer and I used this condition   function isInt a       return  isNaN a   amp  amp  parseInt a     parseFloat a       http   jsfiddle net e267369d 1   Some of the other answers have a similar solution  rely on parseFloat combined with isNaN   but mine should be more straight forward and self explaining     Edit  I found out that my method fails for strings containing comma  like  1 2   and I also realized that in my particular case I want the function to fail if a string is not a valid integer  should fail on any float  even 1 0   So here is my function Mk II   function isInt a       return  isNaN a   amp  amp  parseInt a     parseFloat a   amp  amp   typeof a     string      a indexOf         -1  amp  amp  a indexOf         -1        http   jsfiddle net e267369d 3   Of course in case you actually need the function to accept integer floats  1 0 stuff   you can always remove the dot condition a indexOf         -1

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Add class numOnly for the textbox     document  on  input     numOnly   function e        this value   this value replace    0-9    g          if this value             alert  Integer Number          else        alert  Not an Integer Number                It works for me   Try this one  You can use keypres keyup keydown etc   instead input

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You could check if the number has a remainder   var data   22   if data   1     0         yes it s an integer      Mind you  if your input could also be text and you want to check first it is not  then you can check the type first   var data   22   if typeof data      number            yes it is numeric      if data   1     0             yes it s an integer

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function isInteger argument    return argument      argument      Usage   isInteger 1          true lt br gt  isInteger 0 1        false lt br gt  isInteger  1         true lt br gt  isInteger  0 1       false lt br gt    or   function isInteger argument    return argument    argument   0  amp  amp  argument      argument      Usage   isInteger 1          true lt br gt  isInteger 0 1        false lt br gt  isInteger  1         false lt br gt  isInteger  0 1       false lt br gt

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Use the     operator  strict equality  as below   if  data     parseInt data  10       alert  data is integer   else     alert  data is not an integer

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You could tryNumber isInteger Number value   if value might be an integer in string form e g var value    23  and you want this to evaluate to true  Avoid trying Number isInteger parseInt value   because this won t always return the correct value  e g if var value    23abc  and you use the parseInt implementation  it would still return true   But if you want strictly integer values then probably Number isInteger value  should do the trick

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First off  NaN is a  number   yes I know it s weird  just roll with it   and not a  function    You need to check both if the type of the variable is a number  and to check for integer I would use modulus   alert typeof data      number   amp  amp  data 1    0

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You can use regexp to do this   function isInt data     if typeof data    number        var patt    0-9e           data data         data data match patt       if data  null  return false        else  return true      else return false        It will return false if data isn t an integer  true otherwise

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Why hasnt anyone mentioned Number isInteger      https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Number isInteger  Works perfectly for me and solves the issue with the NaN beginning a number

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ECMA-262 6 0  ES6  standard include Number isInteger function   In order to add support for old browser I highly recommend using strong and community supported solution from   https   github com paulmillr es6-shim  which is pure ES6 JS polyfills library   Note that this lib require es5-shim  just follow README md

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Try the following function   function isInteger  num        return num    parseInt  num 10    amp  amp   isNaN parseInt num       console log   isInteger 42              true console log   isInteger  42             true console log   isInteger 4e2             true console log   isInteger  4e2            true console log   isInteger   1             true console log   isInteger                 false console log   isInteger                 false console log   isInteger 42 1            false console log   isInteger  1a             false console log   isInteger  4e2a           false console log   isInteger null            false console log   isInteger undefined       false console log   isInteger NaN             false     console log   isInteger false             false console log   isInteger true             false console log   isInteger Infinity             false

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From http   www toptal com javascript interview-questions   function isInteger x    return  x 0      x       Found it to be the best way to do this

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To check if integer like poster wants   if   data   parseInt data    return true  else  return false    notice   in front of data  converts string to number   and     for exact   Here are examples   data 10  data   parseInt data  true  data  10   data   parseInt data  true  data  10 2   data   parseInt data  false

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Number isInteger   seems to be the way to go   MDN has also provided the following polyfill for browsers not supporting Number isInteger    mainly all versions of IE   Link to MDN page  Number isInteger   Number isInteger    function value        return typeof value      number   amp  amp              isFinite value   amp  amp              Math floor value      value

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Ok got minus  cause didn t describe my example  so more examples     I use regular expression and test method   var isInteger      0-9  d      isInteger test 123     true isInteger test  123       true isInteger test  sdf      false isInteger test  123sdf      false     If u want to avoid string value  typeof testVal      string   amp  amp  isInteger test testValue

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Number isInteger   is the best way if your browser support it  if not  I think there are so many ways to go   function isInt1 value     return  value 0      value     or   function isInt2 value     return  typeof value      number    amp  amp   value   1     0        or   function isInt3 value     return parseInt value  10      value       or   function isInt4 value     return Math round value      value       now we can test the results   var value   1 isInt1 value       return true isInt2 value       return true isInt3 value       return true isInt4 value       return true  var value   1 1 isInt1 value       return false isInt2 value       return false isInt3 value       return false isInt4 value       return false  var value   1000000000000000000 isInt1 value       return false isInt2 value       return true isInt3 value       return false isInt4 value       return true  var value   undefined isInt1 value       return false isInt2 value       return false isInt3 value       return false isInt4 value       return false  var value    1    number as string isInt1 value       return false isInt2 value       return false isInt3 value       return false isInt4 value       return false   So  all of these methods are works  but when the number is very big  parseInt and   operator would not works well

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For positive integer values without separators   return   data         amp  amp  data     data replace   D            Tests 1  if not empty and 2  if value is equal to the result of a replace of a non-digit char in its value

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Assuming you don t know anything about the variable in question  you should take this approach   if typeof data      number         var remainder    data   1       if remainder     0               yes  it is an integer           else if isNaN remainder                no  data is either  NaN  Infinity  or -Infinity           else              no  it is a float  still a number though          else          no way  it is not even a number     To put it simply   if typeof data    number   amp  amp   data 1    0           data is an integer

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The  accepted  answer is wrong  as some comments below point out   this modification can make it work  if  data toString       parseInt data  10  toString        alert  quot data is a valid integer quot   else     alert  quot data is not a valid integer quot

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Besides  Number isInteger    Maybe Number isSafeInteger   is another option here by using the ES6-specified   To polyfill Number isSafeInteger     in pre-ES6 browsers   Number isSafeInteger   Number isSafeInteger    function num        return typeof num      number   amp  amp              isFinite num   amp  amp              Math floor num      num  amp  amp             Math abs  num    lt   Number MAX SAFE INTEGER

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In ES6 2 new methods are added for Number Object  In it Number isInteger   method returns true if the argument is an integer  Example usage   Number isInteger 10             returns true Number isInteger 10 5           returns false Number isInteger  quot 10 quot            returns false

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This will solve one more scenario  121    a dot at end  function isInt value            var ind   value indexOf               if  ind  gt  -1    return false             if  isNaN value                 return false                     var x   parseFloat value           return  x   0      x

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You can use regexp for this   function isInteger n        return  typeof n     number   amp  amp    -  d    test n

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Use the   operator    5 3   0      5 3      gt  false  5 0   0      5 0      gt  true   So  a test function might look like this   var isInteger   function  value      if  typeof value      number         return false         if   value   0      value        return false         return true

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This solution will work for all browsers  1  Convert your number to string e g  123    String 123   2  Check if there is any   dot  available in given string or not by using indexOf function of string    123  indexOf         -1    integer  123 1  indexOf         3    not integer   OR  Use below function  function isInt val        return String val  indexOf          -1

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Check if the variable is equal to that same variable rounded to an integer  like this   if Math round data     data        alert  Variable is not an integer

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if Number isInteger Number data           -----

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var x   1 5  if  isNaN x     console log  Number     if x   1    0      console log  Integer        else    console log  not a number

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You could use this function   function isInteger value        return  value    parseInt value        It will return true even if the value is a string containing an integer value  So  the results will be   alert isInteger 1       true alert isInteger 1 2       false alert isInteger  1        true alert isInteger  1 2        false alert isInteger  abc        false

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This will output if it is a number if  data  gt   0    data  lt  0               console log  its a number

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Just try this   let number   5  if  Number isInteger number           do something

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My approach  a  gt   1e 21   Only pass for very large numbers  This will cover all cases for sure  unlike other solutions which has been provided in this discussion  a      a 0    if the given function s argument is exactly the same       as the bitwise-transformed value  it means that the argument is an integer  a 0   return 0 for any value of a that isn t a number  and if a is indeed a number  it will strip away anything after the decimal point  so 1 0001 will become 1  x000D   x000D  function isInteger a       return a  gt   1e 21   true   a      a 0         tests                                 1                            true   1000000000000000000000       true   4e2                          true   Infinity                     true   1 0                          true   1 0000000000001              false   0 1                          false    0                           false    1                           false    1 1                         false   NaN                          false                                false                                false   true                         false   false                        false   null                         false   undefined                    false   forEach  a   gt  console log typeof a  a  isInteger a     x000D   x000D   x000D

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That depends  do you also want to cast strings as potential integers as well   This will do   function isInt value      return  isNaN value   amp  amp            parseInt Number value      value  amp  amp             isNaN parseInt value  10        With Bitwise operations  Simple parse and check  function isInt value      var x   parseFloat value     return  isNaN value   amp  amp   x   0      x      Short-circuiting  and saving a parse operation   function isInt value      if  isNaN value         return false        var x   parseFloat value     return  x   0      x      Or perhaps both in one shot   function isInt value      return  isNaN value   amp  amp   function x    return  x   0      x     parseFloat value       Tests   isInt 42            true isInt  42           true isInt 4e2           true isInt  4e2          true isInt   1           true isInt               false isInt               false isInt 42 1          false isInt  1a           false isInt  4e2a         false isInt null          false isInt undefined     false isInt NaN           false   Here s the fiddle  http   jsfiddle net opfyrqwp 28   Performance  Testing reveals that the short-circuiting solution has the best performance  ops sec       Short-circuiting  and saving a parse operation function isInt value      var x    if  isNaN value         return false        x   parseFloat value     return  x   0      x      Here is a benchmark  http   jsben ch   htLVw  If you fancy a shorter  obtuse form of short circuiting   function isInt value      var x    return isNaN value     1    x   parseFloat value    0   x      x       Of course  I d suggest letting the minifier take care of that

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The simplest and cleanest pre-ECMAScript-6 solution  which is also sufficiently robust to return false even if a non-numeric value such as a string or null is passed to the function  would be the following   function isInteger x    return  x 0      x       The following solution would also work  although not as elegant as the one above   function isInteger x    return Math round x      x      Note that Math ceil   or Math floor   could be used equally well  instead of Math round    in the above implementation   Or alternatively   function isInteger x    return  typeof x      number    amp  amp   x   1     0       One fairly common incorrect solution is the following   function isInteger x    return parseInt x  10      x      While this parseInt-based approach will work well for many values of x  once x becomes quite large  it will fail to work properly  The problem is that parseInt   coerces its first parameter to a string before parsing digits  Therefore  once the number becomes sufficiently large  its string representation will be presented in exponential form  e g   1e 21   Accordingly  parseInt   will then try to parse 1e 21  but will stop parsing when it reaches the e character and will therefore return a value of 1  Observe    gt  String 1000000000000000000000   1e 21    gt  parseInt 1000000000000000000000  10  1   gt  parseInt 1000000000000000000000  10      1000000000000000000000 false

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you can also try it this way      var data   22  if  Number isInteger data         console log  integer      else       console log  not an integer         or  if  data     parseInt data  10        console log  integer     else      console log  not an integer

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After few successes and failures  I came up with this solution   const isInt    value    gt      return String parseInt value  10       String value      I liked the idea above of checking the value for not being NaN and use parseFloat  but when I tried it in React infrastructure it didn t work for some reason   Edit  I found a nicer way without using strings   var isInt   function  str      return str      0         str      I think it s the shortest answer  Maybe even the most efficient  but I could be stand corrected

[javascript] How to check if a variable is an integer in JavaScript?

Number.isInteger(data)

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