Check if character is number

Question

I need to check whether justPrices i  substr commapos 2 1    The string is something like   blabla 120   In this case it would check whether  0  is a number  How can this be done

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EDIT  Blender s updated answer is the right answer here if you re just checking a single character  namely  isNaN parseInt c  10     My answer below is a good solution if you want to test whole strings   Here is jQuery s isNumeric implementation  in pure JavaScript   which works against full strings   function isNumeric s        return  isNaN s - parseFloat s        The comment for this function reads         parseFloat NaNs numeric-cast false positives  null true false             but misinterprets leading-number strings  particularly hex literals   0x           subtraction forces infinities to NaN   I think we can trust that these chaps have spent quite a bit of time on this     Commented source here  Super geek discussion here

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Simple function function isCharNumber c      return c  gt    0   amp  amp  c  lt    9

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var Is         character            number   function                    Only computed once             var zero    0  charCodeAt 0   nine    9  charCodeAt 0                return function c                    return  c   c charCodeAt 0    gt   zero  amp  amp  c  lt   nine

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A simple solution by leveraging language s dynamic type checking  function isNumber  string         it has whitespace    if string trim                 return false         return string - 0     string   1     see test cases below  x000D   x000D  function isNumber  str       if str trim                 return false         return str - 0     str   1     console log  -1            isNumber   -1        console log  -1 5            isNumber   -1 5     console log  0            isNumber   0        console log                 isNumber            console log  0 42            isNumber   0 42       console log   42            isNumber    42        console log   abcdef            isNumber    abcdef    console log  1 2 3            isNumber   1 2 3     console log              isNumber           console log  blah            isNumber   blah    x000D   x000D   x000D

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You can use this   function isDigit n        return Boolean  true  true  true  true  true  true  true  true  true  true  n        Here  I compared it to the accepted method  http   jsperf com isdigittest 5   I didn t expect much  so I was pretty suprised  when I found out that accepted method was much slower    Interesting thing is  that while accepted method is faster correct input  eg   5   and slower for incorrect  eg   a    my method is exact opposite  fast for incorrect and slower for correct    Still  in worst case  my method is 2 times faster than accepted solution for correct input and over 5 times faster for incorrect input

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Similar to one of the answers above  I used   var sum   0    some value  let num   parseInt val     or just Number parseInt  if  isNaN num          sum    num       This blogpost sheds some more light on this check if a string is numeric in Javascript   Typescript  amp  ES6

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Try   function is numeric str           try              return isFinite str                    catch err                return false

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If you are testing single characters  then   var isDigit    function         var re      d        return function c            return re test c                 will return true or false depending on whether c is a digit or not

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The shortest solution is    const isCharDigit   n   gt  n  lt  10    You can apply these as well   const isCharDigit   n   gt  Boolean   n    const isCharDigit   n   gt       lt  n  amp  amp  n  lt        const isCharDigit   n   gt      n    if you want to check more than 1 chatacter  you might use next variants  Regular Expression   const isDigit   n   gt    d   test n     Comparison   const isDigit   n   gt   n    n    Check if it is not NaN  const isDigit   n   gt   isNaN n

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You can try this  worked in my case   If you want to test if the first char of a string is an int   if  parseInt YOUR STRING slice 0  1          alert  first char is int     else       alert  first char is not int       If you want to test if the char is a int   if  parseInt YOUR CHAR         alert  first char is int     else       alert  first char is not int

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square   function a        if   a   0     0            return a a        else           return  Enter a valid number              Source

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I suggest a simple regex   If you re looking for just the last character in the string         0-9    test  blabla 120        true       0-9    test  blabla 120a       false       0-9    test  120               true       0-9    test 120                true       0-9    test undefined          false       0-9    test -1                 true       0-9    test  -1                true       0-9    test false              false       0-9    test true               false   And the regex is even simpler if you are just checking a single char as an input   var char    0      0-9    test char                  true

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I think it s very fun to come up with ways to solve this  Below are some   All functions below assume argument is a single character  Change to n 0  to enforce it   Method 1   function isCharDigit n     return   n trim    amp  amp  n  gt  -1      Method 2   function isCharDigit n     return   n trim    amp  amp  n 0  0      Method 3   function isCharDigit n     return   n trim    amp  amp    Number n  1         1  to make it work with     and  0  Chars     Method 4   var isCharDigit    function      var a    1 1 1 1 1 1 1 1 1 1     return function n       return   a n     check if  a  Array has anything in index  n   Cast result to boolean             Method 5   function isCharDigit n     return   n trim    amp  amp   isNaN  n       Test string   var str     90ABcd        char  for  char of str      console log  char  isCharDigit char

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isNumber   function obj  strict        var strict   strict     true   true   false      if  strict            return  isNaN obj   amp  amp  obj instanceof Number   true   false        else           return  isNaN obj - parseFloat obj              output without strict mode   var num   14  var textnum    14   var text    yo   var nan   NaN   isNumber num   isNumber textnum   isNumber text   isNumber nan    true true false false   output with strict mode   var num   14  var textnum    14   var text    yo   var nan   NaN   isNumber num  true   isNumber textnum  true   isNumber text  true   isNumber nan    true false false false

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I wonder why nobody has posted a solution like   var charCodeZero    0  charCodeAt 0   var charCodeNine    9  charCodeAt 0    function isDigitCode n       return n  gt   charCodeZero  amp  amp  n  lt   charCodeNine       with an invocation like   if  isDigitCode justPrices i  charCodeAt commapos 2                 digit   else              not a digit

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This seems to work   Static binding   String isNumeric   function  value        return  isNaN String value    1        Prototype binding   String prototype isNumeric   function          return  isNaN this valueOf     1        It will check single characters  as well as whole strings to see if they are numeric

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Use combination of isNaN and parseInt functions  var character            your character var isDigit     isNaN  parseInt character      Another notable way - multiplication by one  like character   1 instead of parseInt character   - makes a number not only from any numeric string  but also a 0 from empty string and a string containing only spaces so it is not suitable here

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This function works for all test cases that i could find  It s also faster than   function isNumeric  n      if   isNaN parseFloat n    amp  amp  isFinite n   amp  amp   hasLeading0s n         return true        var  n    n    return  n     Infinity     n     -Infinity       x000D   x000D  var isIntegerTest      d     x000D  var isDigitArray     0   0   0   0   0   0   0   0   0   0   x000D   x000D  function hasLeading0s s    x000D    return   typeof s      string     x000D      s length  lt  2    x000D      s 0       0     x000D       isDigitArray s 1      x000D      isIntegerTest test s    x000D    x000D  var isWhiteSpaceTest     s   x000D   x000D  function fIsNaN n    x000D    return   n  lt   0   amp  amp    n  gt  0   x000D    x000D   x000D  function isNumber s    x000D    var t   typeof s  x000D    if  t      number     x000D      return  s  lt   0      s  gt  0   x000D      else if  t      string     x000D      var n    s  x000D      return   fIsNaN n     hasLeading0s s       n     0      s           isWhiteSpaceTest test s      x000D      else if  t      object     x000D      return     s instanceof Number     fIsNaN  s    x000D      x000D    return false  x000D    x000D   x000D  function testRunner IsNumeric    x000D    var total   0  x000D    var passed   0  x000D    var failedTests       x000D   x000D    function test value  result    x000D      total    x000D      if  IsNumeric value      result    x000D        passed    x000D        else   x000D        failedTests push   x000D          value  value  x000D          expected  result x000D            x000D        x000D      x000D       true x000D    test 0  true   x000D    test 1  true   x000D    test -1  true   x000D    test Infinity  true   x000D    test  Infinity   true   x000D    test -Infinity  true   x000D    test  -Infinity   true   x000D    test 1 1  true   x000D    test -0 12e-34  true   x000D    test 8e5  true   x000D    test  1   true   x000D    test  0   true   x000D    test  -1   true   x000D    test  1 1   true   x000D    test  11 112   true   x000D    test   1   true   x000D    test   12e34   true   x000D    test  - 12e34   true   x000D    test   12e-34   true   x000D    test  - 12e-34   true   x000D    test  8e5   true   x000D    test  0x89f   true   x000D    test  00   true   x000D    test  01   true   x000D    test  10   true   x000D    test  0e1   true   x000D    test  0e01   true   x000D    test   0   true   x000D    test  0    true   x000D    test   0e1   true   x000D    test  0 e1   true   x000D    test  0 e00   true   x000D    test  0xf   true   x000D    test  0Xf   true   x000D    test Date now    true   x000D    test new Number 0   true   x000D    test new Number 1e3   true   x000D    test new Number 0 1234   true   x000D    test new Number Infinity   true   x000D    test new Number -Infinity   true   x000D       false x000D    test     false   x000D    test      false   x000D    test false  false   x000D    test  false   false   x000D    test true  false   x000D    test  true   false   x000D    test  99 999   false   x000D    test   abcdef   false   x000D    test  1 2 3   false   x000D    test  blah   false   x000D    test   t t   false   x000D    test   n r   false   x000D    test   r   false   x000D    test NaN  false   x000D    test  NaN   false   x000D    test null  false   x000D    test  null   false   x000D    test new Date    false   x000D    test     false   x000D    test     false   x000D    test new Int8Array    false   x000D    test new Uint8Array    false   x000D    test new Uint8ClampedArray    false   x000D    test new Int16Array    false   x000D    test new Uint16Array    false   x000D    test new Int32Array    false   x000D    test new Uint32Array    false   x000D    test new BigInt64Array    false   x000D    test new BigUint64Array    false   x000D    test new Float32Array    false   x000D    test new Float64Array    false   x000D    test   e0   false   x000D    test      false   x000D    test  00e1   false   x000D    test  01e1   false   x000D    test  00 0   false   x000D    test  01 05   false   x000D    test  00x0   false   x000D    test new Number NaN   false   x000D    test new Number  abc    false   x000D    console log  Passed     passed     of     total     tests     x000D    if  failedTests length  gt  0  console log   x000D      failedTests  failedTests x000D        x000D    x000D  testRunner isNumber  x000D   x000D   x000D

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you can either use parseInt and than check with isNaN  or if you want to work directly on your string you can use regexp like this   function is numeric str       return    d    test str

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Just use isFinite  const number    1   if  isFinite number            do something

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function is numeric mixed var        return  typeof mixed var       number     typeof mixed var       string    amp  amp          mixed var         amp  amp   isNaN mixed var       Source code

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You could use comparison operators to see if it is in the range of digit characters   var c   justPrices i  substr commapos 2 1   if  c  gt    0   amp  amp  c  lt    9            it is a number   else          it isn t

[javascript] Check if character is number?

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