How do you reverse a string in place in JavaScript

Question

How do you reverse a string in place  or in-place  in JavaScript when it is passed to a function with a return statement  without using built-in functions   reverse     charAt   etc

User · Answer

As long as you re dealing with simple ASCII characters  and you re happy to use built-in functions  this will work   function reverse s       return s split     reverse   join          If you need a solution that supports UTF-16 or other multi-byte characters  be aware that this function will give invalid unicode strings  or valid strings that look funny  You might want to consider this answer instead       s  is Unicode aware  a small edit gives -   function reverse s       return     s  reverse   join

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There are many ways you can reverse a string in JavaScript  I m jotting down three ways I prefer   Approach 1  Using reverse function   function reverse str      return str split     reverse   join          Approach 2  Looping through characters   function reverse str      let reversed          for  let character of str        reversed   character   reversed         return reversed      Approach 3  Using reduce function   function reverse str      return str split     reduce  rev  char    gt  char   rev           I hope this helps

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use this method if you are more curious about performance and time complexity  in this method i have divided string in two part and sort it in length 2 times loop iteration    x000D   x000D  let str    abcdefghijklmnopqrstuvwxyz  x000D   x000D  function reverse str   x000D  let store      x000D  let store2      x000D   x000D  for let i str length 2 i gt  0 i--   x000D    if str length 2   0   x000D       store    str charAt i   x000D    store2    str slice  str length 2  1  str length  charAt i  x000D     else  x000D  store    str charAt i-1   x000D    store2    str slice  str length 2   str length  charAt i  x000D      x000D     x000D    x000D  return store2 store x000D    x000D   x000D  console log reverse str   x000D   x000D   x000D    it is not optimal but we can think like this

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You can t because JS strings are immutable  Short non-in-place solution      str  reverse   join      x000D   x000D  let str    Hello World    x000D  let r       str  reverse   join    x000D  console log r   x000D   x000D   x000D

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Here are the four most common methods you can use to achieve a string reversal  Given a string  return a new string with the reversed order of characters  Multiple Solutions to the problem    reverse  apple        leppa    reverse  hello        olleh    reverse  Greetings          sgniteerG      1  First method without using reverse function and negative for loop function reverseFirst str        if str           str    undefined    str     null            const reversedStr               for var i str length  i gt -1  i--            reversedStr push str i                  return reversedStr join     toString                2  Second method using the reverse function function reverseSecond str        return str split     reverse   join            3  Third method using the positive for loop function reverseThird str       const reversedStr           for i 0  i lt str length i              reversedStr push str str length-1-i             return reversedStr join     toString          4  using the modified for loop ES6 function reverseForth str        const reversedStr           for let character of str            reversedStr   character   reversedStr            return reversedStr        5  Using Reduce function function reverse str        return str split     reduce  reversed  character    gt            return character   reversed

User · Answer

This is the easiest way I think   x000D   x000D  var reverse   function str    x000D      var arr       x000D       x000D      for  var i   0  len   str length  i  lt   len  i      x000D          arr push str charAt len - i   x000D        x000D   x000D      return arr join      x000D    x000D   x000D  console log reverse  I want a      x000D   x000D   x000D

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var str    IAMA JavaScript Developer   var a str split      b   a length  for  var i 0  i lt b  i          a unshift a splice 1 i 1  shift      a shift    alert a join

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If you don t want to use any built in function  Try this  var string    abcdefg   var newstring        for let i   0  i  lt  string length  i         newstring   string i     newstring     console log newstring

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word split     reduce  acc  curr    gt  curr    acc

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Keep it DRY and simple silly    function reverse s   let str   s  var reverse       for  var i str length i gt 0 i--        var newstr   str substring 0 i      reverse    newstr substr -1 1    return reverse

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In ECMAScript 6  you can reverse a string even faster without using  split     split method  with the spread operator like so    var str        racecar   reverse   join

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You could can try  const reverse   str   gt  Array from str normalize  NFC    reverse   join       It s not a perfect solution  but it helps deal with characters consisting of multiple code-points  As pointed out  there are issues with maintaining composite and surrogate pair ordering in strings such as  foo  bar ma  ana man ana   Here  is a surrogate pair  and the last n  is a composite pair consisting of two Unicode characters to make up one grapheme  In order to reverse each character  you can use the  reverse   method which is part of the Array prototype  As  reverse   can only be used on an array  the first thing to do is turn the string into an array of characters  Typically   split     is used for this task  however  this splits up surrogate pairs  as already shown in previous answers    gt  gt     split      gt  gt     quot   quot    quot   quot     Instead  if you invoke the String prototype s Symbol iterator method then you ll be able to retain your surrogate pairs within your array   gt  gt           gt  gt    quot  quot    The next thing to handle is any composite characters within the string  Characters which consist of two code points  which are not surrogate pairs  will still be split when iterated on   gt  gt       o         gt  gt    quot o quot    quot    quot    The above separates the base character and the diaresis  which is not desired behaviour  To deal with this  you can use a string method introduced in ES6 known as String prototype normalize    This method can compose the multiple code points into its composed canonical form by using  quot NFC quot  as an argument  This is done by replacing multiple code points with single code points where possible  This allows graphemes consisting of two code points to be represented with one code point   gt  gt       o    normalize  NFC        gt  gt    quot    quot    As this produces one character  it can then be reversed safely when amongst others  Putting both the spread syntax and normalization together  you can successfully reverse strings of characters such as   x000D   x000D  const reverse   str   gt  Array from str normalize  NFC    reverse   join       console log reverse  foo  bar ma  ana man ana     console log reverse  This  emoji is happy     x000D   x000D   x000D    There are a few cases where the above will fail  For instance  the character     heavy black heart      consists of two code points  The first being the heart and the latter being the variation selector-16  U FE0F  which is used to define a glyph variant for the preceding character  Other characters can also produce similar issues like this  Another thing to look out for is ZWJ  Zero-width joiner  characters  which you can find in some scripts  including emoji  For example the emoji    comprises of the Man  Woman and Boy emoji  each separated by a ZWJ  The above reverse   method will not account for this either  One way to fix this is to use Intl Segmenter  which is currently a stage 3 proposal  However  there is a polyfill available for it if you wish to use it  Here is how the reverse   method may look if you use Intl Segmenter  const reverse   str   gt      const segmenter   new Intl Segmenter  quot en quot    granularity   grapheme       const segitr   segmenter segment str     const segarr   Array from segitr    segment     gt  segment  reverse      return segarr join         console log reverse  foo  bar ma  ana man ana        anan am ana  am rab  oof console log reverse  This  emoji is happy        yppah si ijome  sihT console log reverse  Text surrogate pair  composite pair mo  o varient selector     amp  ZWJ              JWZ  amp     rotceles tneirav oo  m riap etisopmoc  riap etagorrus txeT  Currently  Chrome also has its own segmentation API like the one above known as Intl v8BreakIterator  This segmentation API is nonstandard and something that Chrome simply just implements  So  it is subject to change and doesn t work on most browsers  However  if you re curious  this is how it could be done   x000D   x000D  const reverse   str   gt      const iterator   Intl v8BreakIterator   en     type   character       iterator adoptText str     const arr         let pos   iterator first      while  pos     -1        const current   iterator current        const nextPos   iterator next        if  nextPos     -1  break      const slice   str slice current  nextPos       arr unshift slice         return arr join         console log reverse  foo  bar ma  ana man ana        anan am ana  am rab  oof console log reverse  This  emoji is happy        yppah si ijome  sihT console log reverse  Text surrogate pair  composite pair mo  o varient selector     amp  ZWJ              JWZ  amp     rotceles tneirav oo  m riap etisopmoc  riap etagorrus txeT x000D   x000D   x000D

User · Answer

function reverse str   var s       for  var i   str length - 1  i  gt   0  i--       s    str i     return s     reverse  your string comes here

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The following technique  or similar  is commonly used to reverse a string in JavaScript      Don   t use this  var naiveReverse   function string        return string split     reverse   join          In fact  all the answers posted so far are a variation of this pattern  However  there are some problems with this solution  For example   naiveReverse  foo  bar          rab    oof     Where did the    symbol go  Whoops    If you   re wondering why this happens  read up on JavaScript   s internal character encoding   TL DR   is an astral symbol  and JavaScript exposes it as two separate code units    But there   s more      To see which symbols are being used here  check     http   mothereff in js-escapes 1ma C3 B1ana 20man CC 83ana naiveReverse  ma  ana man ana          ana nam ana  am     Wait  so now the tilde is applied to the  a  instead of the  n   WAT    A good string to test string reverse implementations is the following    foo  bar ma  ana man ana    Why  Because it contains an astral symbol     which are represented by surrogate pairs in JavaScript  and a combining mark  the n  in the last man ana actually consists of two symbols  U 006E LATIN SMALL LETTER N and U 0303 COMBINING TILDE    The order in which surrogate pairs appear cannot be reversed  else the astral symbol won   t show up anymore in the    reversed    string  That   s why you saw those    marks in the output for the previous example   Combining marks always get applied to the previous symbol  so you have to treat both the main symbol  U 006E LATIN SMALL LETTER N  as the combining mark  U 0303 COMBINING TILDE  as a whole  Reversing their order will cause the combining mark to be paired with another symbol in the string  That   s why the example output had a  instead of      Hopefully  this explains why all the answers posted so far are wrong     To answer your initial question     how to  properly  reverse a string in JavaScript      I   ve written a small JavaScript library that is capable of Unicode-aware string reversal  It doesn   t have any of the issues I just mentioned  The library is called Esrever  its code is on GitHub  and it works in pretty much any JavaScript environment  It comes with a shell utility binary  so you can easily reverse strings from your terminal if you want   var input    foo  bar ma  ana man ana   esrever reverse input         anan am ana  am rab  oof    As for the    in-place    part  see the other answers

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Something like this should be done following the best practices    x000D   x000D   function    x000D    use strict   x000D   var str    testing   x000D    x000D     using array methods x000D   var arr   new Array    x000D   arr   str split      x000D   arr reverse    x000D   console log arr   x000D    x000D     using custom methods x000D   var reverseString   function str   x000D     x000D    if str    null    str    undefined    str length    0    x000D     return     x000D      x000D     x000D    if str length    1   x000D     return str  x000D      x000D     x000D    var rev       x000D    for var i   0  i  lt  str length  i     x000D     rev i    str str length - 1 - i   x000D      x000D    return rev  x000D      x000D    x000D   console log reverseString str    x000D    x000D        x000D   x000D   x000D

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Another variation  does it work with IE     String prototype reverse   function         for  i 1 s     i lt  this length  s  this substr -i   1          return s      EDIT   This is without the use of built-in functions   String prototype reverse   function         for  i this -1  s     i gt  0  s  this i--          return s      Note  this -1  holds a length of the string   However it s not possible to reverse the string in place  since the assignment to individual array elements doesn t work with String object  protected    I e  you can do assigns  but the resulting string doesn t change

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Detailed analysis and ten different ways to reverse a string and their performance details   http   eddmann com posts ten-ways-to-reverse-a-string-in-javascript   Perfomance of these implementations   Best performing implementation s  per browser   Chrome 15 - Implemations 1 and 6  Firefox 7 - Implementation 6  IE 9 - Implementation 4  Opera 12 - Implementation 9   Here are those implementations   Implementation 1   function reverse s      var o         for  var i   s length - 1  i  gt   0  i--      o    s i     return o      Implementation 2   function reverse s      var o         for  var i   s length - 1  j   0  i  gt   0  i--  j        o j    s i     return o join          Implementation 3   function reverse s      var o         for  var i   0  len   s length  i  lt   len  i        o push s charAt len - i      return o join          Implementation 4   function reverse s      return s split     reverse   join          Implementation 5   function reverse s      var i   s length        o         while  i  gt  0        o    s substring i - 1  i       i--        return o      Implementation 6   function reverse s      for  var i   s length - 1  o       i  gt   0  o    s i--         return o      Implementation 7   function reverse s      return  s                reverse s substr 1     s charAt 0       Implementation 8   function reverse s      function rev s  len  o        return  len     0    o   rev s  --len   o    s len            return rev s  s length           Implementation 9   function reverse s      s   s split        var len   s length        halfIndex   Math floor len   2  - 1        tmp         for  var i   0  i  lt   halfIndex  i              tmp   s len - i - 1           s len - i - 1    s i           s i    tmp                return s join              Implementation 10  function reverse s      if  s length  lt  2      return s    var halfIndex   Math ceil s length   2     return reverse s substr halfIndex              reverse s substr 0  halfIndex

User · Answer

var reverseString   function str      let length   str length - 1    str   str split         for let i 0 i lt   length i         str length   i   1    str length - i          return str splice length   1  join

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Using Array functions   String prototype reverse   function        return    reduceRight call this  function last  secLast  return last   secLast

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Reverse a String using built-in functions   x000D   x000D  function reverse str    x000D       Use the split   method to return a new array x000D        Use the reverse   method to reverse the new created array x000D       Use the join   method to join all elements of the array into a string x000D    return str split     reverse   join      x000D    x000D  console log reverse  hello     x000D   x000D   x000D      Reverse a String without the helpers   x000D   x000D  function reversedOf str    x000D    let newStr       x000D    for  let char of str    x000D      newStr   char   newStr x000D         1st round   h         h  2nd round   e     h     eh      etc   x000D         console log newStr   x000D      x000D    return newStr  x000D    x000D  console log reversedOf  hello     x000D   x000D   x000D

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My own original attempt     var str    The Car    function reverseStr str      var reversed         var len   str length    for  var i   1  i  lt   len   1   i            reversed    str len - i                return reversed     var strReverse   reverseStr str       console log strReverse       raC ehT    http   jsbin com bujiwo 19 edit js console output

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function reverseString string        var reversedString           var stringLength   string length - 1      for  var i   stringLength  i  gt   0  i--            reversedString    string i             return reversedString

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A small function that handles both combining diacritics and 2-byte characters    x000D   x000D   function    x000D    var isCombiningDiacritic   function  code   x000D      x000D      return  0x0300  lt   code  amp  amp  code  lt   0x036F      Comb  Diacritical Marks x000D              0x1AB0  lt   code  amp  amp  code  lt   0x1AFF      Comb  Diacritical Marks Extended x000D              0x1DC0  lt   code  amp  amp  code  lt   0x1DFF      Comb  Diacritical Marks Supplement x000D              0x20D0  lt   code  amp  amp  code  lt   0x20FF      Comb  Diacritical Marks for Symbols x000D              0xFE20  lt   code  amp  amp  code  lt   0xFE2F      Comb  Half Marks x000D   x000D       x000D   x000D    String prototype reverse   function   x000D      x000D      var output       x000D          i        this length - 1  x000D          width  x000D   x000D      for     i  gt   0  --i   x000D        x000D        width   1  x000D        while  i  gt  0  amp  amp  isCombiningDiacritic  this charCodeAt i      x000D          x000D          --i  x000D          width    x000D          x000D   x000D        if   x000D             i  gt  0 x000D           amp  amp    uDC00   lt   this i     amp  amp  this i     lt     uDFFF  x000D           amp  amp    uD800   lt   this i-1   amp  amp  this i-1   lt     uDBFF  x000D          x000D          x000D          --i  x000D          width    x000D          x000D   x000D        output    this substr  i  width    x000D        x000D   x000D      return output  x000D      x000D        x000D   x000D     Tests x000D    x000D     abcdefg   x000D     ab u0303c   x000D     a uD83C uDFA5b   x000D     a uD83C uDFA5b uD83C uDFA6c   x000D     a uD83C uDFA5b u0306c uD83C uDFA6d   x000D     TO         TH E     P   O  N Y      copied from http   stackoverflow com a 1732454 1509264 x000D    forEach  x000D    function str   console log  str     - gt      str reverse        x000D     x000D     x000D   x000D   x000D      Update  A more complete list of combining diacritics is         var isCombiningDiacritic   function  code                   return  0x0300  lt   code  amp  amp  code  lt   0x036F                  0x0483  lt   code  amp  amp  code  lt   0x0489                  0x0591  lt   code  amp  amp  code  lt   0x05BD                  code    0x05BF                  0x05C1  lt   code  amp  amp  code  lt   0x05C2                  0x05C4  lt   code  amp  amp  code  lt   0x05C5                  code    0x05C7                  0x0610  lt   code  amp  amp  code  lt   0x061A                  0x064B  lt   code  amp  amp  code  lt   0x065F                  code    0x0670                  0x06D6  lt   code  amp  amp  code  lt   0x06DC                  0x06DF  lt   code  amp  amp  code  lt   0x06E4                  0x06E7  lt   code  amp  amp  code  lt   0x06E8                  0x06EA  lt   code  amp  amp  code  lt   0x06ED                  code    0x0711                  0x0730  lt   code  amp  amp  code  lt   0x074A                  0x07A6  lt   code  amp  amp  code  lt   0x07B0                  0x07EB  lt   code  amp  amp  code  lt   0x07F3                  code    0x07FD                  0x0816  lt   code  amp  amp  code  lt   0x0819                  0x081B  lt   code  amp  amp  code  lt   0x0823                  0x0825  lt   code  amp  amp  code  lt   0x0827                  0x0829  lt   code  amp  amp  code  lt   0x082D                  0x0859  lt   code  amp  amp  code  lt   0x085B                  0x08D3  lt   code  amp  amp  code  lt   0x08E1                  0x08E3  lt   code  amp  amp  code  lt   0x0902                  code    0x093A                  code    0x093C                  0x0941  lt   code  amp  amp  code  lt   0x0948                  code    0x094D                  0x0951  lt   code  amp  amp  code  lt   0x0957                  0x0962  lt   code  amp  amp  code  lt   0x0963                  code    0x0981                  code    0x09BC                  0x09C1  lt   code  amp  amp  code  lt   0x09C4                  code    0x09CD                  0x09E2  lt   code  amp  amp  code  lt   0x09E3                  0x09FE  lt   code  amp  amp  code  lt   0x0A02                  code    0x0A3C                  0x0A41  lt   code  amp  amp  code  lt   0x0A51                  0x0A70  lt   code  amp  amp  code  lt   0x0A71                  code    0x0A75                  0x0A81  lt   code  amp  amp  code  lt   0x0A82                  code    0x0ABC                  0x0AC1  lt   code  amp  amp  code  lt   0x0AC8                  code    0x0ACD                  0x0AE2  lt   code  amp  amp  code  lt   0x0AE3                  0x0AFA  lt   code  amp  amp  code  lt   0x0B01                  code    0x0B3C                  code    0x0B3F                  0x0B41  lt   code  amp  amp  code  lt   0x0B44                  0x0B4D  lt   code  amp  amp  code  lt   0x0B56                  0x0B62  lt   code  amp  amp  code  lt   0x0B63                  code    0x0B82                  code    0x0BC0                  code    0x0BCD                  code    0x0C00                  code    0x0C04                  0x0C3E  lt   code  amp  amp  code  lt   0x0C40                  0x0C46  lt   code  amp  amp  code  lt   0x0C56                  0x0C62  lt   code  amp  amp  code  lt   0x0C63                  code    0x0C81                  code    0x0CBC                  0x0CCC  lt   code  amp  amp  code  lt   0x0CCD                  0x0CE2  lt   code  amp  amp  code  lt   0x0CE3                  0x0D00  lt   code  amp  amp  code  lt   0x0D01                  0x0D3B  lt   code  amp  amp  code  lt   0x0D3C                  0x0D41  lt   code  amp  amp  code  lt   0x0D44                  code    0x0D4D                  0x0D62  lt   code  amp  amp  code  lt   0x0D63                  code    0x0DCA                  0x0DD2  lt   code  amp  amp  code  lt   0x0DD6                  code    0x0E31                  0x0E34  lt   code  amp  amp  code  lt   0x0E3A                  0x0E47  lt   code  amp  amp  code  lt   0x0E4E                  code    0x0EB1                  0x0EB4  lt   code  amp  amp  code  lt   0x0EBC                  0x0EC8  lt   code  amp  amp  code  lt   0x0ECD                  0x0F18  lt   code  amp  amp  code  lt   0x0F19                  code    0x0F35                  code    0x0F37                  code    0x0F39                  0x0F71  lt   code  amp  amp  code  lt   0x0F7E                  0x0F80  lt   code  amp  amp  code  lt   0x0F84                  0x0F86  lt   code  amp  amp  code  lt   0x0F87                  0x0F8D  lt   code  amp  amp  code  lt   0x0FBC                  code    0x0FC6                  0x102D  lt   code  amp  amp  code  lt   0x1030                  0x1032  lt   code  amp  amp  code  lt   0x1037                  0x1039  lt   code  amp  amp  code  lt   0x103A                  0x103D  lt   code  amp  amp  code  lt   0x103E                  0x1058  lt   code  amp  amp  code  lt   0x1059                  0x105E  lt   code  amp  amp  code  lt   0x1060                  0x1071  lt   code  amp  amp  code  lt   0x1074                  code    0x1082                  0x1085  lt   code  amp  amp  code  lt   0x1086                  code    0x108D                  code    0x109D                  0x135D  lt   code  amp  amp  code  lt   0x135F                  0x1712  lt   code  amp  amp  code  lt   0x1714                  0x1732  lt   code  amp  amp  code  lt   0x1734                  0x1752  lt   code  amp  amp  code  lt   0x1753                  0x1772  lt   code  amp  amp  code  lt   0x1773                  0x17B4  lt   code  amp  amp  code  lt   0x17B5                  0x17B7  lt   code  amp  amp  code  lt   0x17BD                  code    0x17C6                  0x17C9  lt   code  amp  amp  code  lt   0x17D3                  code    0x17DD                  0x180B  lt   code  amp  amp  code  lt   0x180D                  0x1885  lt   code  amp  amp  code  lt   0x1886                  code    0x18A9                  0x1920  lt   code  amp  amp  code  lt   0x1922                  0x1927  lt   code  amp  amp  code  lt   0x1928                  code    0x1932                  0x1939  lt   code  amp  amp  code  lt   0x193B                  0x1A17  lt   code  amp  amp  code  lt   0x1A18                  code    0x1A1B                  code    0x1A56                  0x1A58  lt   code  amp  amp  code  lt   0x1A60                  code    0x1A62                  0x1A65  lt   code  amp  amp  code  lt   0x1A6C                  0x1A73  lt   code  amp  amp  code  lt   0x1A7F                  0x1AB0  lt   code  amp  amp  code  lt   0x1B03                  code    0x1B34                  0x1B36  lt   code  amp  amp  code  lt   0x1B3A                  code    0x1B3C                  code    0x1B42                  0x1B6B  lt   code  amp  amp  code  lt   0x1B73                  0x1B80  lt   code  amp  amp  code  lt   0x1B81                  0x1BA2  lt   code  amp  amp  code  lt   0x1BA5                  0x1BA8  lt   code  amp  amp  code  lt   0x1BA9                  0x1BAB  lt   code  amp  amp  code  lt   0x1BAD                  code    0x1BE6                  0x1BE8  lt   code  amp  amp  code  lt   0x1BE9                  code    0x1BED                  0x1BEF  lt   code  amp  amp  code  lt   0x1BF1                  0x1C2C  lt   code  amp  amp  code  lt   0x1C33                  0x1C36  lt   code  amp  amp  code  lt   0x1C37                  0x1CD0  lt   code  amp  amp  code  lt   0x1CD2                  0x1CD4  lt   code  amp  amp  code  lt   0x1CE0                  0x1CE2  lt   code  amp  amp  code  lt   0x1CE8                  code    0x1CED                  code    0x1CF4                  0x1CF8  lt   code  amp  amp  code  lt   0x1CF9                  0x1DC0  lt   code  amp  amp  code  lt   0x1DFF                  0x20D0  lt   code  amp  amp  code  lt   0x20F0                  0x2CEF  lt   code  amp  amp  code  lt   0x2CF1                  code    0x2D7F                  0x2DE0  lt   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var str    my name is saurabh    var empStr    finalString     var chunk     function reverse str   var i j 0 n str length      for i 0 i lt n   i           if str i                      chunk j  empStr              empStr                   j             else              empStr empStr str i                       for var z chunk length-1 z gt  0 z--           finalString   finalString       chunk z           console log finalString             return true    reverse str

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Strings themselves are immutable  but you can easily create a reversed copy with the following code   function reverseString str       var strArray   str split        strArray reverse       var strReverse   strArray join         return strReverse     reverseString  hello

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You could try something like this  I m sure there s some room for refactoring  I couldn t get around using the split function  Maybe someone knows of a way to do it without split   Code to set up  can put this in your  js library  Code to use it  has client side code  only because it was tested in a browser    var sentence    My Stack is Overflowing   document write sentence reverseLetters       lt br   gt     document write sentence reverseWords       lt br   gt       Snippet    x000D   x000D  String prototype aggregate   function vals  aggregateFunction    x000D   x000D    var temp       x000D    for  var i   vals length - 1  i  gt   0  i--    x000D      temp   aggregateFunction vals i   temp   x000D      x000D    return temp  x000D    x000D   x000D  String prototype reverseLetters   function     x000D    return this aggregate this split      x000D      function current  word    x000D        return word   current  x000D         x000D    x000D   x000D  String prototype reverseWords   function     x000D    return this aggregate this split       x000D      function current  word    x000D        return word         current  x000D         x000D    x000D   x000D  var sentence    My Stack is Overflowing   x000D  document write sentence reverseLetters       lt br   gt     x000D  document write sentence reverseWords       lt br   gt     x000D   x000D   x000D

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Seems like I m 3 years late to the party     Unfortunately you can t as has been pointed out  See Are JavaScript strings immutable  Do I need a  quot string builder quot  in JavaScript   The next best thing you can do is to create a  view  or  wrapper   which takes a string and reimplements whatever parts of the string API you are using  but pretending the string is reversed  For example   var identity   function x  return x    function LazyString s        this original   s       this length   s length      this start   0  this stop   this length  this dir   1      virtual  slicing         dir -1 if reversed       this  caseTransform   identity        syntactic sugar to create new object  function S s        return new LazyString s        We now implement a        reversed  which toggles a flag which will change our math    function       begin anonymous scope     var x   LazyString prototype          Addition to the String API     x reversed   function             var s   new LazyString this original            s start   this stop - this dir          s stop   this start - this dir          s dir   -1 this dir          s length   this length           s  caseTransform   this  caseTransform          return s           We also override string coercion for some extra versatility  not really necessary           OVERRIDE STRING COERCION          - for string concatenation e g   abc  reversed  abc       x toString   function             if  typeof this  realized     undefined         cached  to avoid recalculation             this  realized   this dir  1                   this original slice this start this stop                     this original slice this stop 1 this start 1  split     reverse   join                   this  realized   this  caseTransform call this  realized  this  realized                     return this  realized           Now we reimplement the String API by doing some math          String API          Do some math to figure out which character we really want      x charAt   function i            return this slice i  i 1  toString              x charCodeAt   function i              return this slice i  i 1  toString   charCodeAt 0             Slicing functions       x slice   function start stop               lazy chaining version of https   developer mozilla org en-US docs JavaScript Reference Global Objects Array slice          if  stop   undefined              stop   this length           var relativeStart   start lt 0   this length start   start          var relativeStop   stop lt 0   this length stop   stop           if  relativeStart  gt   this length              relativeStart   this length          if  relativeStart  lt  0              relativeStart   0           if  relativeStop  gt  this length              relativeStop   this length          if  relativeStop  lt  0              relativeStop   0           if  relativeStop  lt  relativeStart              relativeStop   relativeStart           var s   new LazyString this original           s length   relativeStop - relativeStart          s start   this start   this dir relativeStart          s stop   s start   this dir s length          s dir   this dir             console log  this start this stop this dir this length    s start s stop s dir s length            s  caseTransform   this  caseTransform          return s            x substring   function                              x substr   function                             Miscellaneous functions          Iterative search      x indexOf   function value            for var i 0  i lt this length  i                if  value  this charAt i                   return i          return -1            x lastIndexOf   function             for var i this length-1  i gt  0  i--              if  value  this charAt i                   return i          return -1                The following functions are too complicated to reimplement easily         Instead just realize the slice and do it the usual non-in-place way       x match   function             var s   this toString            return s apply s  arguments             x replace   function             var s   this toString            return s apply s  arguments             x search   function             var s   this toString            return s apply s  arguments             x split   function             var s   this toString            return s apply s  arguments             Case transforms       x toLowerCase   function             var s   new LazyString this original           s  caseTransform      toLowerCase           s start this start  s stop this stop  s dir this dir  s length this length           return s            x toUpperCase   function             var s   new LazyString this original           s  caseTransform      toUpperCase           s start this start  s stop this stop  s dir this dir  s length this length           return s                 end anonymous scope   Demo    gt  r   S  abcABC   LazyString   original   abcABC      proto    LazyString   gt  r charAt 1            doesn t reverse string     good if very long   B    gt  r toLowerCase         must reverse string  so does so  cbacba    gt  r toUpperCase         string already reversed  no extra work  CBACBA    gt  r    -demo-    r      natural coercion  string already reversed  no extra work  CBAcba-demo-CBAcba    The kicker -- the following is done in-place by pure math  visiting each character only once  and only if necessary    gt   demo      S  0123456789abcdef   slice 3  reversed   slice 1 -1  toUpperCase    demo  EDCBA987654    gt  S  0123456789ABCDEF   slice 3  reversed   slice 1 -1  toLowerCase   charAt 3   b    This yields significant savings if applied to a very large string  if you are only taking a relatively small slice thereof   Whether this is worth it  over reversing-as-a-copy like in most programming languages  highly depends on your use case and how efficiently you reimplement the string API  For example if all you want is to do string index manipulation  or take small slices or substrs  this will save you space and time  If you re planning on printing large reversed slices or substrings however  the savings may be small indeed  even worse than having done a full copy  Your  reversed  string will also not have the type string  though you might be able to fake this with prototyping   The above demo implementation creates a new object of type ReversedString  It is prototyped  and therefore fairly efficient  with almost minimal work and minimal space overhead  prototype definitions are shared   It is a lazy implementation involving deferred slicing  Whenever you perform a function like  slice or  reversed  it will perform index mathematics  Finally when you extract data  by implicitly calling  toString   or  charCodeAt      or something   it will apply those in a  smart  manner  touching the least data possible   Note  the above string API is an example  and may not be implemented perfectly  You also can use just 1-2 functions which you need

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First  use Array from   to turn a string into an array  then Array prototype reverse   to reverse the array  and then Array prototype join   to make it back a string   const reverse   str   gt  Array from str  reverse   join

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No built-in methods  Given that strings in Javascript are immutable  you probably want to use the in-built methods like split  join  and so on  But here are two ways to go without those methods   function ReverseString str        var len   str length      var newString            while  len--            newString push str len               return newString join         console log ReverseString  amgod      dogma  function RecursiveStringReverse str  len        if  len     undefined          len   str length - 1       if  len  gt  0          return str len    RecursiveReverse str  --len        return str len      console log RecursiveStringReverse  Hello  world        dlrow  olleH

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OK  pretty simple  you can create a function with a simple loop to do the string reverse for you without using reverse    charAt   etc like this   For example you have this string   var name    StackOverflow     Create a function like this  I call it reverseString     function reverseString str      if  str trim       string      typeof str        return        let l str length  s       while l  gt  0        l--      s   str l         return s      And you can call it like   reverseString name     And the result will be    wolfrevOkcatS

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It is not possible to reverse a string in place  but it is possible to do it not in place

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The whole  reverse a string in place  is an antiquated interview question C programmers  and people who were interviewed by them  for revenge  maybe    will ask   Unfortunately  it s the  In Place  part that no longer works because strings in pretty much any managed language  JS  C   etc  uses immutable strings  thus defeating the whole idea of moving a string without allocating any new memory   While the solutions above do indeed reverse a string  they do not do it without allocating more memory  and thus do not satisfy the conditions   You need to have direct access to the string as allocated  and be able to manipulate its original memory location to be able to reverse it in place   Personally  i really hate these kinds of interview questions  but sadly  i m sure we ll keep seeing them for years to come

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Adding to the String prototype is ideal  just in case it gets added into the core JS language   but you first need to check if it exists  and add it if it doesn t exist  like so   String prototype reverse   String prototype reverse    function          return this split     reverse   join

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During an interview  I was asked to reverse a string without using any variables or native methods  This is my favorite implementation   function reverseString str        return str               reverseString str slice 1     str 0

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es6   array from const reverseString    string    gt  Array from string  reduce  a  e    gt  e   a     split const reverseString    string    gt  string split     reduce  a  e    gt  e   a       split problem    split     0      Array from     0                  gt  false    split     0      Array from     0                  gt  false

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I know that this is an old question that has been well answered  but for my own amusement I wrote the following reverse function and thought I would share it in case it was useful for anyone else   It handles both surrogate pairs and combining marks   function StringReverse  str      var charArray         for  var i   0  i  lt  str length  i                if  i 1  lt  str length                      var value   str charCodeAt i             var nextValue   str charCodeAt i 1             if         value  gt   0xD800  amp  amp  value  lt   0xDBFF                    amp  amp   nextValue  amp  0xFC00     0xDC00     Surrogate pair                    nextValue  gt   0x0300  amp  amp  nextValue  lt   0x036F      Combining marks                             charArray unshift str substring i  i 2                  i       Skip the other half               continue                                    Otherwise we just have a rogue surrogate marker or a plain old character        charArray unshift str i             return charArray join          All props to Mathias  Punycode  and various other references for schooling me on the complexities of character encoding in JavaScript

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var str    sample string      map call str  function x      return x     reverse   join        OR  var str    sample string   console log str split     reverse   join            Output   gnirts elpmas

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Added for reverse of string without loop  it s working through recursion   x000D   x000D  function reverse y       if y length  1    y length    0            return y            return y split     y length - 1   reverse y slice 0  y length-1      console log reverse  Hello     x000D   x000D   x000D

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The real answer is  you can t reverse it in place  but you can create a new string that is the reverse   Just as an exercise to play with recursion   sometimes when you go to an interview  the interviewer may ask you how to do this using recursion  and I think the  preferred answer  might be  I would rather not do this in recursion as it can easily cause a stack overflow   because it is O n  rather than O log n   If it is O log n   it is quite difficult to get a stack overflow -- 4 billion items could be handled by a stack level of 32  as 2    32 is 4294967296   But if it is O n   then it can easily get a stack overflow   Sometimes the interviewer will still ask you   just as an exercise  why don t you still write it using recursion    And here it is   String prototype reverse   function         if  this length  lt   1  return this      else return this slice 1  reverse     this slice 0 1       test run   var s       for var i   0  i  lt  1000  i          s      apple    i     console log s reverse       output   999elppa899elppa   2elppa1elppa0elppa   To try getting a stack overflow  I changed 1000 to 10000 in Google Chrome  and it reported   RangeError  Maximum call stack size exceeded

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We can iterate the string array from both the ends  start and end  and swap at each iteration  function reverse str     let strArray   str split  quot  quot     let start   0   let end   strArray length - 1    while start  lt   end      let temp   strArray start     strArray start    strArray end     strArray end    temp     start      end--      return strArray join  quot  quot       Although the number of operations have reduced  its time complexity is still O n  as the number of operations still scale linearly with the size of input  Ref  AlgoDaily

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The below might help anyone that is looking to reverse a string recursively  Was asked to do this in a recent job interview using functional programming style   var reverseStr   function str        return  str length  gt  0    str str length - 1    reverseStr str substr 0  str length -   1               tests console log reverseStr  setab retsam       master bates

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There are Multiple ways of doing it  you may check the following   1  Traditional for loop incrementing     x000D   x000D  function reverseString str   x000D          let stringRev      x000D          for let i  0  i lt str length  i     x000D              stringRev   str i  stringRev  x000D            x000D          return stringRev  x000D    x000D  alert reverseString  Hello World      x000D   x000D   x000D    2  Traditional for loop decrementing     x000D   x000D  function reverseString str   x000D      let revstr       x000D      for let i   str length-1  i gt  0  i--   x000D          revstr   revstr  str i   x000D        x000D      return revstr  x000D    x000D  alert reverseString  Hello World      x000D   x000D   x000D    3  Using for-of loop   x000D   x000D  function reverseString str   x000D      let strn      x000D      for let char of str   x000D          strn   char   strn  x000D        x000D      return strn  x000D    x000D  alert reverseString  Get well soon     x000D   x000D   x000D    4  Using the forEach  high order array method    x000D   x000D  function reverseString str   x000D   x000D    let revSrring       x000D    str split     forEach function char   x000D       x000D      revSrring   char   revSrring  x000D     x000D        x000D    return revSrring  x000D    x000D  alert reverseString  Learning JavaScript     x000D   x000D   x000D    5  ES6 standard    x000D   x000D  function reverseString str   x000D   x000D    let revSrring       x000D    str split     forEach char   gt  revSrring   char   revSrring   x000D    return revSrring  x000D    x000D  alert reverseString  Learning JavaScript     x000D   x000D   x000D    6  The latest way    x000D   x000D  function reverseString str   x000D   x000D    return str split     reduce function revString  char   x000D         return char   revString  x000D            x000D    x000D    x000D   x000D  alert reverseString  Learning JavaScript     x000D   x000D   x000D    7  You may also get the result using the following    x000D   x000D  function reverseString str   x000D   x000D    return str split     reduce  revString  char   gt  char   revString       x000D    x000D    x000D  alert reverseString  Learning JavaScript     x000D   x000D   x000D

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I think String prototype reverse is a good way to solve this problem  the code as below   String prototype reverse   function       return this split     reverse   join         var str    this is a good example for string reverse   str reverse    - gt   esrever gnirts rof elpmaxe doog a si siht

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I guess  this will work for you  function reverse str       str   str split     reverse   join     split      reverse   join           console log str

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String prototype reverse string function    return this split     reverse   join         or  String prototype reverse string   function         var s           var i   this length      while  i gt 0            s    this substring i-1 i           i--            return s

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Here s a basic ES6 immutable example without using Array prototype reverse    x000D   x000D        reverse   String - gt  String x000D  const reverse   s   gt     reduceRight call s   a  b    gt  a   b  x000D   x000D  console log reverse  foo         gt   oof  x000D  console log reverse  bar         gt   rab  x000D  console log reverse  foo-bar         gt   rab-oof  x000D   x000D   x000D

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Best ways to reverse a string in JavaScript  1  Array reverse   You   re probably thinking  wait I thought we were reversing a string  why are you using the Array reverse method  Using the String split method we are converting our string into an Array of characters  Then we are reversing the order of each value in the array and then finally we convert the Array back to a String using the Array join method   function reverseString str        return str split     reverse   join        reverseString  dwayne      2  Decrementing while-loop   Although pretty verbose  this solution does have its advantages over solution one  You   re not creating an array and you   re just concatenating a string based on characters from the source string   From a performance perspective  this one would probably yield the best results  although untested   For extremely long strings  the performance gains might drop out the window though   function reverseString str        var temp           var i   str length       while  i  gt  0            temp    str substring i - 1  i           i--              return temp    reverseString  dwayne      3  Recursion  I love how simple and clear this solution is  You can clearly see that the String charAt and String substr methods are being used to pass through a different value by calling itself each time until the string is empty of which the ternary would just return an empty string instead of using recursion to call itself  This would probably yield the second best performance after the second solution   function reverseString str        return  str                reverseString str substr 1     str charAt 0     reverseString  dwayne

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function reverse string string    var string   var len   string length   var stringExp   string split      var i  for  i   len-1  i  gt  0 i--    var result   document write stringExp i       return result     reverse string  This is a reversed string        outputs  gnirts desrever a si sihT

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In ES6  you have one more option  function reverseString  str      return     str  reverse   join        reverseString  Hello

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x000D   x000D      function reverse string  x000D        x000D      let arr       x000D      for let char of string    x000D        arr unshift char   x000D        x000D      let rev   arr join     x000D      return rev x000D        x000D       x000D      let result   reverse  hello   x000D      console log result  x000D   x000D   x000D

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Legible way using spread operator   x000D   x000D  const reverseString   str   gt      str  reverse   join       console log reverseString  ABC     x000D   x000D   x000D

User · Answer

without converting string to array   String prototype reverse   function          var ret           var size   0       for  var i   this length - 1  -1  lt  i  i -  size             if               uD800   lt   this i - 1   amp  amp  this i - 1   lt     uDBFF   amp  amp               uDC00   lt   this i       amp  amp  this i       lt     uDFFF                          size   2              ret    this i - 1    this i             else               size   1              ret    this i                        return ret     console log  ana nam ana  am       ma  ana man ana  reverse       using Array reverse without converting characters to code points   String prototype reverse   function          var array   this split     reverse         for  var i   0  i  lt  this length    i             if               uD800   lt   this i - 1   amp  amp  this i - 1   lt     uDBFF   amp  amp               uDC00   lt   this i       amp  amp  this i       lt     uDFFF                          array i - 1    array i - 1    array i               array i    array i - 1  substr 0  1               array i - 1    array i - 1  substr 1  1                         return array join         console log  ana nam ana  am       ma  ana man ana  reverse

[javascript] How do you reverse a string in place in JavaScript?

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