How to perform case-insensitive sorting in JavaScript

Question

I have an array of strings I need to sort in JavaScript  but in a case-insensitive way  How to perform this

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arr sort function a b        a   a toLowerCase        b   b toLowerCase        if  a    b  return 0      if  a  gt  b  return 1      return -1        In above function  if we just compare when lower case two value a and b  we will not have the pretty result   Example  if array is  A  a  B  b  c  C  D  d  e  E  and we use the above function  we have exactly that array  It s not changed anything   To have the result is  A  a  B  b  C  c  D  d  E  e   we should compare again when two lower case value is equal   function caseInsensitiveComparator valueA  valueB        var valueALowerCase   valueA toLowerCase        var valueBLowerCase   valueB toLowerCase         if  valueALowerCase  lt  valueBLowerCase            return -1        else if  valueALowerCase  gt  valueBLowerCase            return 1        else     valueALowerCase     valueBLowerCase         if  valueA  lt  valueB                return -1            else if  valueA  gt  valueB                return 1            else               return 0

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ES6 version    quot Foo quot    quot bar quot   sort  a  b    gt  a localeCompare b   en     sensitivity   base       Source  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects String localeCompare

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I wrapped the top answer in a polyfill so I can call  sortIgnoreCase   on string arrays     Array sortIgnoreCase   polyfill if   Array prototype sortIgnoreCase        Array prototype sortIgnoreCase   function              return this sort function  a  b                return a toLowerCase   localeCompare b toLowerCase

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Normalize the case in the  sort   with  toLowerCase

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If you want to guarantee the same order regardless of the order of elements in the input array  here is a stable sorting   myArray sort function a  b           Storing case insensitive comparison        var comparison   a toLowerCase   localeCompare b toLowerCase            If strings are equal in case insensitive comparison        if  comparison     0               Return case sensitive comparison instead            return a localeCompare b                Otherwise return result        return comparison

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Wrap your strings in    i  This is an easy way to use regex to ignore casing

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It is time to revisit this old question   You should not use solutions relying on toLowerCase  They are inefficient and simply don t work in some languages  Turkish for instance   Prefer this     Foo    bar   sort  a  b    gt  a localeCompare b  undefined   sensitivity   base       Check the documentation for browser compatibility and all there is to know about the sensitivity option

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myArray sort    function a  b        if  a toLowerCase    lt  b toLowerCase    return -1      if  a toLowerCase    gt  b toLowerCase    return 1      return 0           EDIT  Please note that I originally wrote this to illustrate the technique rather than having performance in mind  Please also refer to answer  Ivan Krechetov for a more compact solution

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This may help if you have struggled to understand   var array     sort    Me    alphabetically    But    Ignore    case    console log  Unordered array ---   array   ------------     array sort function a b        a   a toLowerCase        b   b toLowerCase        console log  Compare      a      and      b              if  a    b            console log  Comparison result  0 --- leave as is             return 0            if  a  gt  b            console log  Comparison result  1 --- move   b   to before   a               return 1            console log  Comparison result  -1 --- move   a   to before   b           return -1         console log  Ordered array ---   array   ------------         return logic       If compareFunction a  b  is less than 0  sort a to a lower index than b  i e  a comes first  If compareFunction a  b  returns 0  leave a and b unchanged with respect to each other  but sorted with respect to all different elements  Note  the ECMAscript standard does not guarantee this behaviour  and thus not all browsers  e g  Mozilla versions dating back to at least 2003  respect this  If compareFunction a  b  is greater than 0  sort b to a lower index than a         http   jsfiddle net ianjamieson wmxn2ram 1

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arr sort function a b        a   a toLowerCase        b   b toLowerCase        if  a    b  return 0      if  a  gt  b  return 1      return -1

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The other answers assume that the array contains strings  My method is better  because it will work even if the array contains null  undefined  or other non-strings   var notdefined  var myarray     a    c   null  notdefined   nulk    BYE    nulm     myarray sort ignoreCase    alert JSON stringify myarray          show the result  function ignoreCase a b        return     a  toUpperCase    lt      b  toUpperCase     -1   1      The null will be sorted between  nulk  and  nulm   But the undefined will be always sorted last

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In support of the accepted answer I would like to add that the function below seems to change the values in the original array to be sorted so that not only will it sort lower case but upper case values will also be changed to lower case  This is a problem for me because even though I wish to see Mary next to mary  I do not wish that the case of the first value Mary be changed to lower case   myArray sort    function a  b        if  a toLowerCase    lt  b toLowerCase    return -1      if  a toLowerCase    gt  b toLowerCase    return 1      return 0           In my experiments  the following function from the accepted answer sorts correctly but does not change the values     Foo    bar   sort function  a  b        return a toLowerCase   localeCompare b toLowerCase

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You can also use the new Intl Collator   compare  per MDN it s more efficient when sorting arrays  The downside is that it s not supported by older browsers  MDN states that it s not supported at all in Safari  Need to verify it  since it states that Intl Collator is supported       When comparing large numbers of strings  such as in sorting large arrays  it is better to create an Intl Collator object and use the function provided by its compare property     Foo    bar   sort Intl Collator   compare       bar    Foo

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You can also use the Elvis operator   arr     Bob    charley    fudge    Fudge    biscuit    arr sort function s1  s2       var l s1 toLowerCase    m s2 toLowerCase        return l   m 0 l gt m 1 -1      console log arr     Gives   biscuit Bob charley fudge Fudge   The localeCompare method is probably fine though     Note  The Elvis operator is a short form  ternary operator  for if then else  usually with assignment  If you look at the    sideways  it looks like Elvis    i e  instead of   if  y      x   1    else     x   2      you can use   x   y 1 2    i e  when y is true  then return 1  for assignment to x   otherwise return 2  for assignment to x

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In  almost    a one-liner     Foo    bar   sort function  a  b        return a toLowerCase   localeCompare b toLowerCase           Which results in     bar    Foo      While    Foo    bar   sort      results in     Foo    bar

[javascript] How to perform case-insensitive sorting in JavaScript?

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