How to do case insensitive string comparison

Question

How do I perform case insensitive string comparison in JavaScript

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As said in recent comments  string  localeCompare supports case insensitive comparisons  among other powerful things    Here s a simple example   xyz  localeCompare  XyZ   undefined    sensitivity   base         returns 0   And a generic function you could use  function equalsIgnoringCase text  other        return text localeCompare other  undefined    sensitivity   base         0      Note that instead of undefined you should probably enter the specific locale you are working with  This is important as denoted in the MDN docs     in Swedish     and a are separate base letters   Sensitivity options    Browser support  As of time of posting  UC Browser for Android and Opera Mini do not support locale and options parameters  Please check https   caniuse com  search localeCompare for up to date info

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If both strings are of the same known locale  you may want to use Intl Collator object like this   function equalIgnoreCase s1  string  s2  string        return new Intl Collator  en-US     sensitivity   base     compare s1  s2      0      Obviously  you may want to cache the Collator for better efficiency   The advantages of this approach is that it should be much faster than using RegExps and is based on an extremely customizable  see description of locales and options constructor parameters in the article above  set of ready-to-use collators

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With the help of regular expression also we can achieve     keyword i  test source     i is for ignore case  If not necessary we can ignore and test for NOT case sensitive match like    keyword   test source

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Remember that casing is a locale specific operation  Depending on scenario you may want to take that in to account  For example  if you are comparing names of two people you may want to consider locale but if you are comparing machine generated values such as UUID then you might not  This why I use following function in my utils library  note that type checking is not included for performance reason    function compareStrings  string1  string2  ignoreCase  useLocale        if  ignoreCase            if  useLocale                string1   string1 toLocaleLowerCase                string2   string2 toLocaleLowerCase                      else               string1   string1 toLowerCase                string2   string2 toLowerCase                         return string1     string2

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EDIT  This answer was originally added 9 years ago  Today you should use localeCompare with the sensitivity   accent  option    x000D   x000D  function ciEquals a  b    x000D      return typeof a      string   amp  amp  typeof b      string  x000D            a localeCompare b  undefined    sensitivity   accent         0 x000D            a     b  x000D    x000D   x000D  console log   a     a     ciEquals  a    a     x000D  console log   AaA     aAa     ciEquals  AaA    aAa     x000D  console log   a            ciEquals  a           x000D  console log   a     b     ciEquals  a    b     x000D   x000D   x000D    The   sensitivity   accent    tells localeCompare   to treat two variants of the same base letter as the same unless they have different accents  as in the third example  above   Alternatively  you can use   sensitivity   base     which treats two characters as equivalent as long as their base character is the same  so A would be treated as equivalent to       Note that the third parameter of localeCompare is not supported in IE10 or lower or certain mobile browsers  see the compatibility chart on the page linked above   so if you need to support those browsers  you ll need some kind of fallback   function ciEqualsInner a  b        return a localeCompare b  undefined    sensitivity   accent         0     function ciEquals a  b        if  typeof a      string     typeof b      string             return a     b                     v--- feature detection     return ciEqualsInner  A    a             ciEqualsInner a  b                fallback approach here          Original answer  The best way to do a case insensitive comparison in JavaScript is to use RegExp match   method with the i flag     Case-insensitive search  When both strings being compared are variables  not constants   then it s a little more complicated  cause you need to generate a RegExp from the string but passing the string to RegExp constructor can result in incorrect matches or failed matches if the string has special regex characters in it   If you care about internationalization don t use toLowerCase   or toUpperCase   as it doesn t provide accurate case-insensitive comparisons in all languages   http   www i18nguy com unicode turkish-i18n html

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I wrote a extension  very trivial  if  typeof String prototype isEqual    function         String prototype isEqual   function  str           return this toUpperCase    str toUpperCase

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Use RegEx for string match or comparison   In JavaScript  you can use match   for string comparison  don t forget to put iin RegEx   Example   var matchString    Test   if  matchString match  test i       alert  String matched      else    alert  String not matched

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There are two ways for case insensitive comparison    Convert strings to upper case and then compare them using the strict operator        How strict operator treats operands read stuff at  http   www thesstech com javascript relational-logical-operators Pattern matching using string methods    Use the  search  string method for case insensitive search  Read about search and other string methods at  http   www thesstech com pattern-matching-using-string-methods    lt  doctype html gt     lt html gt       lt head gt         lt script gt              1st way          var a    apple           var b    APPLE             if  a toUpperCase       b toUpperCase                alert  equal                         2nd way          var a     Null and void           document write a search  null i             lt  script gt       lt  head gt   lt  html gt

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Since no answer clearly provided a simple code snippet for using RegExp  here s my attempt   function compareInsensitive str1  str2      return typeof str1      string   amp  amp       typeof str2      string   amp  amp       new RegExp       str1 replace   -                    g       amp            i   test str2       It has several advantages    Verifies parameter type  any non-string parameter  like undefined for example  would crash an expression like str1 toUpperCase     Does not suffer from possible internationalization issues  Escapes the RegExp string

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If you know you re dealing with ascii text then you can just use a uppercase lowercase character offset comparison   Just make sure the string your  perfect  string  the one you want to match against  is lowercase   const CHARS IN BETWEEN   32  const LAST UPPERCASE CHAR   90     Z function strMatchesIgnoreCase lowercaseMatch  value        let i   0  matches   lowercaseMatch length     value length      while  matches  amp  amp  i  lt  lowercaseMatch length            const a   lowercaseMatch charCodeAt i           const A   a - CHARS IN BETWEEN          const b   value charCodeAt i           const B   b     b  gt  LAST UPPERCASE CHAR    -CHARS IN BETWEEN   CHARS IN BETWEEN           matches   a     b    lowerA     b                A     b    upperA    b                a     B    lowerA     b                A     B     upperA     b         i              return matches

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Lots of answers here  but I like to add a sollution based on extending the String lib   String prototype equalIgnoreCase   function str        return  str    null               amp  amp  typeof str      string               amp  amp  this toUpperCase       str toUpperCase         This way you can just use it like you do in Java   Example   var a    hello   var b    HeLLo   var c    world    if  a equalIgnoreCase b         document write  a    b      if  a equalIgnoreCase c         document write  a    c      if   b equalIgnoreCase c         document write  b    c        Output will be    a    b   b    c     x000D   x000D  String prototype equalIgnoreCase   function str    x000D    return  str    null  amp  amp  x000D      typeof str      string   amp  amp  x000D      this toUpperCase       str toUpperCase     x000D    x000D   x000D   x000D  var a    hello   x000D  var b    HeLLo   x000D  var c    world   x000D   x000D  if  a equalIgnoreCase b     x000D    document write  a    b    x000D    document write   lt br gt     x000D    x000D  if  a equalIgnoreCase c     x000D    document write  a    c    x000D    x000D  if   b equalIgnoreCase c     x000D    document write  b    c    x000D    x000D   x000D   x000D

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How about NOT throwing exceptions and NOT using slow regex   return str1    null  amp  amp  str2    null       amp  amp  typeof str1      string   amp  amp  typeof str2      string       amp  amp  str1 toUpperCase       str2 toUpperCase      The above snippet assumes you don t want to match if either string is null or undefined   If you want to match null undefined  then   return  str1    null  amp  amp  str2    null          str1    null  amp  amp  str2    null           amp  amp  typeof str1      string   amp  amp  typeof str2      string           amp  amp  str1 toUpperCase       str2 toUpperCase       If for some reason you care about undefined vs null   return  str1     undefined  amp  amp  str2     undefined          str1     null  amp  amp  str2     null          str1    null  amp  amp  str2    null           amp  amp  typeof str1      string   amp  amp  typeof str2      string           amp  amp  str1 toUpperCase       str2 toUpperCase

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I have recently created a micro library that provides case-insensitive string helpers  https   github com nickuraltsev ignore-case   It uses toUpperCase internally    var ignoreCase   require  ignore-case     ignoreCase equals  FOO    Foo         gt  true ignoreCase startsWith  foobar    FOO         gt  true ignoreCase endsWith  foobar    BaR         gt  true ignoreCase includes  AbCd    c         gt  true ignoreCase indexOf  AbCd    c         gt  2

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The simplest way to do it  if you re not worried about special Unicode characters  is to call toUpperCase   var areEqual   string1 toUpperCase       string2 toUpperCase

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This is an improved version of this answer   String equal   function  s1  s2  ignoreCase  useLocale        if  s1    null    s2    null          return false       if   ignoreCase            if  s1 length     s2 length              return false           return s1     s2             if  useLocale            if  useLocale length              return s1 toLocaleLowerCase useLocale      s2 toLocaleLowerCase useLocale          else             return s1 toLocaleLowerCase       s2 toLocaleLowerCase             else           if  s1 length     s2 length              return false           return s1 toLowerCase       s2 toLowerCase                Usages  amp  tests    x000D   x000D  String equal   function  s1  s2  ignoreCase  useLocale    x000D      if  s1    null    s2    null  x000D          return false  x000D   x000D      if   ignoreCase    x000D          if  s1 length     s2 length  x000D              return false  x000D   x000D          return s1     s2  x000D        x000D   x000D      if  useLocale    x000D          if  useLocale length  x000D              return s1 toLocaleLowerCase useLocale      s2 toLocaleLowerCase useLocale  x000D          else x000D              return s1 toLocaleLowerCase       s2 toLocaleLowerCase   x000D        x000D      else   x000D          if  s1 length     s2 length  x000D              return false  x000D   x000D          return s1 toLowerCase       s2 toLowerCase    x000D        x000D    x000D   x000D     If you don t mind extending the prototype  x000D  String prototype equal   function string2  ignoreCase  useLocale    x000D    return String equal this valueOf    string2  ignoreCase  useLocale   x000D    x000D   x000D     ------------------ TESTS ---------------------- x000D  console log  Tests       x000D   x000D  console log  Case sensitive 1    x000D  var result    Abc123  equal  Abc123    x000D  console assert result     true   x000D   x000D  console log  Case sensitive 2    x000D  result    aBC123  equal  Abc123    x000D  console assert result     false   x000D   x000D  console log  Ignore case    x000D  result    AbC123  equal  aBc123   true   x000D  console assert result     true   x000D   x000D  console log  Ignore case   Current locale    x000D  result    AbC123  equal  aBc123   true   x000D  console assert result     true   x000D   x000D  console log  Turkish test 1  ignore case  en-US     x000D  result    IiiI  equal  iiII   true   en-US    x000D  console assert result     false   x000D   x000D  console log  Turkish test 2  ignore case  tr-TR     x000D  result    IiiI  equal  iiII   true   tr-TR    x000D  console assert result     true   x000D   x000D  console log  Turkish test 3  case sensitive  tr-TR     x000D  result    IiiI  equal  iiII   false   tr-TR    x000D  console assert result     false   x000D   x000D  console log  null-test-1    x000D  result    AAA  equal null   x000D  console assert result     false   x000D   x000D  console log  null-test-2    x000D  result   String equal null   BBB    x000D  console assert result     false   x000D   x000D  console log  null-test-3    x000D  result   String equal null  null   x000D  console assert result     false   x000D   x000D   x000D

User · Answer

if you are concerned about the direction of the inequality  perhaps you want to sort a list  you pretty-much have to do case-conversion  and as there are more lowercase characters in unicode than uppercase toLowerCase is probably the best conversion to use   function my strcasecmp  a  b          if  a     toLowerCase    gt   b     toLowerCase    return 1       if  a     toLowerCase    lt   b     toLowerCase    return -1     return 0     Javascript seems to use locale  C  for string comparisons so the resulting ordering will be ugly if the strings contain other than ASCII letters  there s not much that can be done about that without doing much more detailed inspection of the strings

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Even this question have already answered  I have a different approach to use RegExp and match to ignore case sensitive  Please see my link  https   jsfiddle net marchdave 7v8bd7dq 27       btnGuess   click guessWord      function guessWord         var letter       guessLetter   val       var word    ABC      var pattern   RegExp letter   gi       pattern   a gi     var result   word match pattern      alert  Ignore case sensitive     result

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For better browser compatibility you can rely on a regular expression  This will work in all web browsers released in the last 20 years  String prototype equalsci   function s        var regexp   RegExp  quot   quot  this replace                       lt  gt   -  g   quot     amp  quot    quot   quot    quot i quot        return regexp test s       quot PERSON    EXAMPLE COM quot  equalsci  quot person    example com quot     returns true  This is different from the other answers found here because it takes into account that not all users are using modern web browsers  Note  If you need to support unusual cases like the Turkish language you will need to use localeCompare because i and I are not the same letter in Turkish   quot I quot  localeCompare  quot i quot   undefined    sensitivity  quot accent quot      0   returns true  quot I quot  localeCompare  quot i quot    quot tr quot     sensitivity  quot accent quot      0   returns false

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I like this quick shorthand variation -   export const equalsIgnoreCase    str1  str2    gt        return   str1  amp  amp   str2      str1  amp  amp  str2  amp  amp  str1 toUpperCase      str2 toUpperCase        Quick in processing  and does what it is intended to

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Suppose we want to find the string variable needle in the string variable haystack  There are three gotchas    Internationalized applications should avoid string toUpperCase and string toLowerCase  Use a regular expression which ignores case instead  For example  var needleRegExp   new RegExp needle   i    followed by needleRegExp test haystack   In general  you might not know the value of needle  Be careful that needle does not contain any regular expression special characters  Escape these using needle replace   -                   s  g       amp      In other cases  if you want to precisely match needle and haystack  just ignoring case  make sure to add     at the start and     at the end of your regular expression constructor    Taking points  1  and  2  into consideration  an example would be    var haystack    A  BAIL  Of  Hay    var needle    bail    var needleRegExp   new RegExp needle replace   -                   s  g       amp      i    var result   needleRegExp test haystack   if  result           Your code here

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Convert both to lower  only once for performance reasons  and compare them with ternary operator in a single line   function strcasecmp s1 s2       s1  s1     toLowerCase        s2  s2     toLowerCase        return s1 gt s2 1  s1 lt s2 -1 0

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str    Lol   str2    lOl   regex   new RegExp       str         i    if  regex test str         console log  true

[javascript] How to do case insensitive string comparison?

Sensitivity options

Browser support

Examples related to javascript

Examples related to string