How can I test if a letter in a string is uppercase or lowercase using JavaScript

Question

User · Answer

This checks the ENTIRE string  not just the first letter   I thought I d share it with everyone here   Here is a function that uses a regular expression to test against the letters of a string  it returns true if the letter is uppercase  A-Z    We then reduce the true false array to a single value   If it is equal to the length of the string  that means all the letters passed the regex test  which means the string is uppercase   If not  the string is lowercase   const isUpperCase    str    gt      let result   str      split          map letter   gt    A-Z   test letter        reduce  a  b    gt  a   b      return result     str length     console log isUpperCase  123        false console log  123       123  toUpperCase        true

User · Answer

Stephen Nelsons  function converted to a prototype with lots of test examples   I ve also added whole strings to the function for completeness   See code for additional comments    x000D   x000D     Please note  there s no requirement to trim any leading or trailing white x000D  spaces  This will remove any digits in the whole string example returning the x000D  correct result     x000D   x000D  String prototype isUpperCase   function arg    x000D  var re   new RegExp    s   d   s     g    x000D  if  arg wholeString   return this replace re         this replace re      toUpperCase    else x000D  return   this  amp  amp  this    this toLocaleLowerCase    x000D    x000D   x000D  console log   r nString prototype isUpperCase  whole string examples    x000D  console log   DDD is       DDD  isUpperCase    wholeString true       x000D  console log  9 is      9  isUpperCase    wholeString true       x000D  console log  Aa is      Aa  isUpperCase    wholeString true       x000D  console log  DDD 9 is      DDD 9  isUpperCase    wholeString true       x000D  console log  DDD is      DDD  isUpperCase    wholeString true       x000D  console log  Dll is      Dll  isUpperCase    wholeString true       x000D  console log  ll is      ll  isUpperCase    wholeString true       x000D   x000D  console log   r nString prototype isUpperCase  non-whole string examples  will only string on a  charAt n  basis  Defaults to the first character    x000D  console log   DDD is       DDD  isUpperCase    wholeString false       x000D  console log  9 is      9  isUpperCase    wholeString false       x000D  console log  Aa is      Aa  isUpperCase    wholeString false       x000D  console log  DDD 9 is      DDD 9  isUpperCase    wholeString false       x000D  console log  DDD is      DDD  isUpperCase    wholeString false       x000D  console log  Dll is      Dll  isUpperCase    wholeString false       x000D  console log  ll is      ll  isUpperCase    wholeString false       x000D   x000D  console log   r nString prototype isUpperCase  single character examples    x000D  console log  BLUE CURA  AO  charAt 9      is      BLUE CURA  AO  charAt 9  isUpperCase    wholeString false       x000D  console log  9 is      9  isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log  A is      A  isUpperCase    wholeString false       x000D  console log  d is      d  isUpperCase    wholeString false       x000D  console log  E is      E  isUpperCase    wholeString false       x000D  console log     is          isUpperCase    wholeString false       x000D  console log     is          isUpperCase    wholeString false       x000D  console log     is          isUpperCase    wholeString false       x000D  console log     is          isUpperCase    wholeString false       x000D  console log     is          isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D  console log    is         isUpperCase    wholeString false       x000D   x000D   x000D

User · Answer

This is straightforward  readable solution using a simple regex      Get specific char in string const char   string charAt index    const isLowerCaseLetter      a-z   test char    const isUpperCaseLetter      A-Z   test char

User · Answer

You can also use a regular expression to explicitly detect uppercase roman alphabetical characters    isUpperCase   function char      return     A-Z   exec char 0           EDIT  the above function is correct for ASCII Basic Latin Unicode  which is probably all you ll ever care about  The following version also support Latin-1 Supplement and Greek and Coptic Unicode blocks    In case you needed that for some reason   isUpperCase   function char      return     A-Z  -    -    -  -             -    exec char 0         This strategy starts to fall down if you need further support  is   uppercase   since some blocks intermix upper and lowercase characters

User · Answer

function isCapital ch       return ch charCodeAt    gt   65  amp  amp  ch charCodeAt    lt   90

User · Answer

More specifically to what is being asked  Pass in a String and a position to check  Very close to Josh s except that this one will compare a larger string  Would have added as a comment but I don t have that ability yet   function isUpperCase myString  pos         return  myString charAt pos     myString charAt pos  toUpperCase            function isLowerCase myString  pos        return  myString charAt pos     myString charAt pos  toLowerCase

User · Answer

The answer by josh and maleki will return true on both upper and lower case if the character or the whole string is numeric  making the result a false result  example using josh   var character    5   if  character    character toUpperCase       alert   upper case true      if  character    character toLowerCase      alert   lower case true        another way is to test it first if it is numeric  else test it if upper or lower case example   var strings    this iS a TeSt 523 Now    var i 0  var character     while  i  lt   strings length       character   strings charAt i       if   isNaN character   1            alert  character is numeric         else          if  character    character toUpperCase                  alert   upper case true                      if  character    character toLowerCase                 alert   lower case true                        i

User · Answer

The problem with the other answers is  that some characters like numbers or punctuation also return true when checked for lowercase uppercase   I found this to work very well for it   function isLowerCase str        return str    str toLowerCase    amp  amp  str    str toUpperCase        This will work for punctuation  numbers and letters   assert isLowerCase  a    assert  isLowerCase        assert  isLowerCase  4    assert  isLowerCase         To check one letter just call it using isLowerCase str charIndex

User · Answer

See my comment on the chosen answer  Other solutions that limit to the ASCII table or use the actual character literals completely ignore Unicode and the several hundred other characters there that have case   This code will set the caseGroup variable to    1 for Upper Case -1 for Lower Case 0 for Without Case  var caseGroup    character toLowerCase      character toUpperCase     0    character    character toUpperCase     1   -1       You could bake that into something like this         function determineCase character            return  character toLowerCase      character toUpperCase     0    character    character toUpperCase     1   -1               function isUpper character            return determineCase character     1             function isLower character            return determineCase character     -1             function hasCase character            return determineCase character     0

User · Answer

Another way is to compare the character with an empty object  i don t really know s why it works  but it works    for  let i   1  i  lt   26  i         const letter    i   9  toString 36  toUpperCase       console log  letter   letter   is upper   letter lt         returns true   for  let i   1  i  lt   26  i         const letter    i   9  toString 36      console log  letter   letter   is upper   letter lt         returns false     so in a function    function charIsUpper character       return character lt         EDIT  it doesn t work with accents and diacritics  so it s possible to remove it  function charIsUpper character       return character             normalize  NFD               replace    u0300- u036f  g      lt

User · Answer

const isUpperCase    string    gt     A-Z     test string    then     isUpperCase  A      true isUpperCase  a      false

User · Answer

You can test if your array has an upper case or lower case string by using the match          method and regex  below is just a basic foundation to start your test     var array     a    b    c    A    B    C                   -                var character   array join           console log character     var test   function search         upperCase   search match   A-Z  g        console log upperCase         lowerCase   search match   a-z  g        console log lowerCase           test character

User · Answer

You can also use this  it will check the string for lower and uppercase  var s    a  if   a-z   test s      alert   lower case true       if   A-Z   test s      alert   upper case true

User · Answer

function checkCase c       var u   c toUpperCase        return  c toLowerCase       u   -1    c     u   1   0         Based on Sonic Beard comment to the main answer  I changed the logic in the result    0  Lowercase 1  Uppercase -1  neither

User · Answer

A good answer to this question should be succinct  handle unicode correctly  and deal with empty strings and nulls   function isUpperCase c        return   c  amp  amp  c    c toLocaleLowerCase        This approach deals with empty strings and nulls first  then ensures that converting the given string to lower case changes its equality  This ensures that the string contains at least one capital letter according to the current local s capitalisation rules  and won t return false positives for numbers and other glyphs that don t have capitalisation    The original question asked specifically about testing the first character  In order to keep your code simple and clear I d split the first character off the string separately from testing whether it s upper case

User · Answer

The best way is to use a regular expression  a ternary operator  and the built in  test   method for strings    I leave you to Google the ins and outs of regular expressions and the test method for strings  they re easy to find   but here we ll use it to test your variable     a-z  i test your-character-here    This will return TRUE of FALSE based on whether or not your character matches the character set in the regular expression  Our regular expression checks for all letters a-z   a-z   regardless of their case thanks to the i flag   So  a basic test would be   var theAnswer       if    a-z  i test your-character-here       theAnswer    It s a letter       Now we need to determine if it s upper or lower case  So  if we remove the i flag from our regular expression  then our code above will test for lower case letters a-z  And if we stick another if statement in the else of our first if statement  we can test for upper case too by using A-Z  Like this   var theAnswer       if    a-z   test your-character-here       theAnswer    It s a lower case letter     else if    A-Z   test your-character-here       theAnswer    It s an upper case letter        And just in case it s not a letter  we can add a final else statement   var theAnswer       if    a-z   test your-character-here       theAnswer    It s a lower case letter     else if    A-Z   test your-character-here       theAnswer    It s an upper case letter      else     theAnswer    It s not a letter       The above code would work  But it s kinda ugly  Instead  we can use a  ternary operator  to replace our if-else statements above  Ternary operators are just shorthand simple ways of coding an if-else  The syntax is easy    statement-to-be-evaluated     code-if-true     code-if-false    And these can be nested within each other  too  So a function might look like   var theAnswer       function whichCase theLetter      theAnswer     a-z   test theLetter     It s lower case           theAnswer     A-Z   test theLetter     It s upper case           return theAnswer       The above code looks good  but won t quite work  because if our character is lower case  theAnswer gets set to    when it test for uppercase  so lets nest them   var theAnswer       function whichCase theLetter      theAnswer     a-z   test theLetter     It s lower case        A-Z   test theLetter     It s upper case      It s not a letter       return theAnswer       That will work great  But there s no need to have two seperate lines for setting the variable theAnswer and then returning it  And we should be using let and const rather than var  look those up if you re not sure why   Once we make those changes   function whichCase theLetter      return   A-Z   test theLetter     It s upper case        a-z   test theLetter     It s lower case      It s not a letter           And we end up with an elegant  concise piece of code

User · Answer

This question has clearly been answered a number of times  but i thought i d share my solution as I haven t seen it in the given answers   var lower case   function letter       lowers    abcdefghijklmnopqrstuvwxyz       return letter     letter toLowerCase    amp  amp  lowers indexOf letter   gt   0     var upper case   function letter       uppers    ABCDEFGHIJKLMNOPQRSTUVWXYZ       return letter     letter toUpperCase    amp  amp  uppers indexOf letter   gt   0      2

User · Answer

Simply check the ASCII value     IsLower verify that a string does not contains upper char func IsLower str string  bool       for i    range str           ascii    int str i           if ascii  lt  91  amp  amp  ascii  gt  64               return false                     return true

User · Answer

This is how I did it recently   1  Check that a char string s is lowercase  s toLowerCase      s  amp  amp  s toUpperCase      s  2  Check s is uppercase  s toUpperCase      s  amp  amp  s toLowerCase      s  Covers cases where s contains non-alphabetic chars and diacritics

User · Answer

One I use  notice this doesnt make  TestString  as  T est String  or   Test String     function seperateCapitalised capitalisedString        if  typeof capitalisedString      string     capitalisedString length     0          return capitalisedString       var newStr   capitalisedString 0       for  var i   1  i  lt  capitalisedString length  i              var char   capitalisedString i            if  char     char toUpperCase    amp  amp  isNaN char                 newStr          char                    else               newStr    char                      return newStr

User · Answer

You could utilize a regular expression test and the toUpperCase method   String prototype charAtIsUpper   function  atpos         var chr   this charAt atpos         return   A-Z    u0080- u024F   test chr   amp  amp  chr     chr toUpperCase          usage  note  character position is zero based   hi There  charAtIsUpper 3            gt  true  BLUE CURA  AO  charAtIsUpper 9        gt  true  Hello  World   charAtIsUpper 5       gt  false   See also

User · Answer

Assuming that a string is only considered to not be all uppercase if at least one lowercase letter is present  this works fine  I understand it s not concise and succinct like everybody else tried to do  but does it works     function isUpperCase str        for  var i   0  len   str length  i  lt  len  i              var letter   str charAt i           var keyCode   letter charCodeAt i           if  keyCode  gt  96  amp  amp  keyCode  lt  123                return false                       return true

User · Answer

function solution s    var c   s 0    if  c    c toUpperCase    amp  amp    c  gt    0   amp  amp  c  lt    9    amp  amp  c  gt   A   amp  amp  c  lt    Z          return  upper     else if  c    c toLowerCase    amp  amp    c  gt    0   amp  amp  c  lt    9    amp  amp  c  gt   a   amp  amp  c  lt    z         return  lower     else if  c  gt    0   amp  amp  c  lt    9       return  digit    else     return  other        var str1   solution  A       upper var str2   solution  b      lower var str3   solution  1      digit var str4   solution         other console log    str1    str2    str3    str4

User · Answer

function isUpperCase myString       return  myString    myString toUpperCase         function isLowerCase myString       return  myString    myString toLowerCase

User · Answer

if  character    character toLowerCase           The character is lowercase   else        The character is uppercase

User · Answer

This will log true if character is uppercase letter  and log false in every other case   var letters     a    b    c    A    B    C                   -                  for  var  i   0  i lt letters length  i          if  letters i      letters i  toUpperCase            amp  amp  letters i      letters i  toLowerCase              console log letters i           true         else           console log letters i           false              You may test it here  http   jsfiddle net Axfxz   use Firebug or sth       for  var  i   0  i lt letters length  i          if  letters i      letters i  toUpperCase            amp  amp  letters i      letters i  toLowerCase              console log letters i           true         else           console log letters i           false              and this is for lowercase

User · Answer

function checkCharType  charToCheck           body         var returnValue    O       var charCode   charToCheck charCodeAt 0        if charCode  gt    A  charCodeAt 0   amp  amp  charCode  lt    Z  charCodeAt 0             returnValue    U         else if  charCode  gt    a  charCodeAt 0   amp  amp                  charCode  lt    z  charCodeAt 0             returnValue    L        else if  charCode  gt    0  charCodeAt 0   amp  amp              charCode  lt    9  charCodeAt 0               returnValue    N             return returnValue     var myString   prompt  Enter Some text      Hello world       switch  checkCharType myString         case  U              statements 1         document write  First character was upper case            break       case  L           document write  First character was a lower case            break      case  N           document write  First character was a number            break     default             statements def         document write  First character was not a character or a number            break       Define a Function checkCharType   By declaring the variable returnValue and initialising it to the Character  O  to indicate it s Some other value   U for uppercase  L for Lowercase   N for number  Use the charCodeAt   method to get the character code of the first character   Using if Statement   which check within what range of values the character code falls   If it falls between the character codes for A and Z  Its Uppercase  character code between a and z  Its Lowercase  and so on    A  charCode 0      var myChar   new String  A     myChar charCodeAt 0    A    number code  65    Check the String

User · Answer

There s a really simple answer  which nobody else has mentioned   function isLowerCase str        return str     str toUpperCase        If str toUpperCase   does not return the same str  it has to be lower case  To test for upper case you change it to str     str toLowererCase     Unlike some other answers  it works correctly on non-alpha characters  returns false  and it works for other alphabets  accented characters etc

User · Answer

I need to test against a string of any character  including white space  marks  numbers  unicode characters      Because white space  numbers  marks    will be the same in both upper case and lower case  and I want to find real upper case letters  I do this   let countUpperCase   0  let i   0  while  i  lt   string length      const character   string charAt i     if  character     character toUpperCase    amp  amp  character     character toLowerCase          countUpperCase          i

[javascript] How can I test if a letter in a string is uppercase or lowercase using JavaScript?

Examples related to javascript