Fastest method to replace all instances of a character in a string

Question

What is the fastest way to replace all instances of a string character in a string in JavaScript  A while  a for-loop  a regular expression

User · Answer

I tried a number of these suggestions after realizing that an implementation I had written of this probably close to 10 years ago actually didn't work completely (nasty production bug in an long-forgotten system, isn't that always the way?!)... what I noticed is that the ones I tried (I didn't try them all) had the same problem as mine, that is, they wouldn't replace EVERY occurrence, only the first, at least for my test case of getting "test....txt" down to "test.txt" by replacing ".." with "."... maybe I missed so regex situation? But I digress...

So, I rewrote my implementation as follows. It's pretty darned simple, although I suspect not the fastest but I also don't think the difference will matter with modern JS engines, unless you're doing this inside a tight loop of course, but that's always the case for anything...

function replaceSubstring(inSource, inToReplace, inReplaceWith) {

  var outString = inSource;
  while (true) {
    var idx = outString.indexOf(inToReplace);
    if (idx == -1) {
      break;
    }
    outString = outString.substring(0, idx) + inReplaceWith +
      outString.substring(idx + inToReplace.length);
  }
  return outString;

}

Hope that helps someone!

User · Answer

Gumbo adding extra answer - user email replace  foo gi  bar       foo g - Refers to the all string to replace matching the case sensitive   foo gi - Refers to the without case sensitive and replace all For Eg   Foo  foo  FoO  fOO    DEMO

User · Answer

var mystring    This is a string   var newString   mystring replace  i g   a      newString now is  Thas as a strang

User · Answer

Find  Replace  Case    i e  Test to see if this works   Yes No   replaceAll   Yes No     Yes        i e 2  Test to see if this works   Yes No   replaceAll   yes no     Yes    true   String prototype replaceAll   function  f   r   c       var o   this toString      var r         var s   o    var b   0    var e   -1    if  c    f    f toLowerCase    s   o toLowerCase         while  e s indexOf  f    gt  -1          r    o substring b  b e     r      s   s substring e  f length  s length       b    e  f length            Add Leftover   if s length gt 0   r  o substring o length-s length  o length           Return New String   return r

User · Answer

Use the replace   method of the String object   As mentioned in the selected answer  the  g flag should be used in the regex  in order to replace all instances of the substring in the string

User · Answer

You can use the following   newStr   str replace    a-z0-9  gi          or  newStr   str replace    a-zA-Z0-9  g          This is going to replace all the character that are not letter or numbers to        Simple change the underscore value for whatever you want to replace it

User · Answer

Try this replaceAll  http   dumpsite com forum index php topic 4 msg8 msg8  String prototype replaceAll   function str1  str2  ignore         return this replace new RegExp str1 replace                                        lt   gt  -  amp    g      amp     ignore  gi   g     typeof str2    string   str2 replace     g         str2        It is very fast  and it will work for ALL these conditions that many others fail on    x  replaceAll  x    xyz       xyz   x  replaceAll      xyz       xyzxxyz   aA  replaceAll  a    b   true      bb   Hello     replaceAll               Hello      Let me know if you can break it  or you have something better  but make sure it can pass these 4 tests

User · Answer

I just coded a benchmark and tested the first 3 answers  It seems that for short strings   lt 500 characters  the third most voted answer is faster than the second most voted one   For long strings  add   repeat 300   to the test string  the faster is answer 1 followed by the second and the third   Note        The above is true for browsers using v8 engine  chrome chromium etc     With firefox  SpiderMonkey engine  the results are totally different   Check for yourselves     Firefox with the third solution seems to be   more than 4 5 times faster than Chrome with the first solution    crazy  D    x000D   x000D  function log data    x000D    document getElementById  log   textContent    data     n   x000D    x000D   x000D  benchmark         gt    x000D   x000D    time function   function ms  f  num    x000D      var z  x000D      var t   new Date   getTime    x000D      for  z   0  x000D          new Date   getTime   - t   lt  ms   z    f num   x000D      return  z   ms  x000D         returns how many times the function was run in  ms  milliseconds  x000D   x000D   x000D    function benchmark     x000D      function compare a  b    x000D        if  a 1   gt  b 1     x000D          return -1  x000D          x000D        if  a 1   lt  b 1     x000D          return 1  x000D          x000D        return 0  x000D        x000D   x000D         functions x000D   x000D      function replace1 s    x000D        s replace  foo g   bar   x000D        x000D   x000D  String prototype replaceAll2   function  f   r    x000D   x000D    var o   this toString    x000D    var r       x000D    var s   o  x000D    var b   0  x000D    var e   -1  x000D          if  c    f    f toLowerCase    s   o toLowerCase      x000D   x000D    while  e s indexOf  f    gt  -1  x000D      x000D      r    o substring b  b e     r  x000D      s   s substring e  f length  s length   x000D      b    e  f length  x000D      x000D   x000D       Add Leftover x000D    if s length gt 0   r  o substring o length-s length  o length     x000D   x000D       Return New String x000D    return r  x000D     x000D   x000D  String prototype replaceAll   function str1  str2  ignore    x000D        return this replace new RegExp str1 replace                                        lt   gt  -  amp    g       amp      ignore    gi     g      typeof str2      string     str2 replace     g            str2   x000D        x000D   x000D      function replace2 s    x000D        s replaceAll  foo    bar   x000D        x000D   x000D      function replace3 s    x000D        s split  foo   join  bar    x000D        x000D   x000D      function replace4 s    x000D        s replaceAll2  foo    bar   x000D        x000D   x000D   x000D      funcs     x000D         replace1  0   x000D         replace2  0   x000D         replace3  0   x000D         replace4  0  x000D         x000D   x000D      funcs forEach  ff    gt    x000D        console log  Benchmarking      ff 0  name   x000D        ff 1    time function 2500  ff 0    foOfoobarBaR barbarfoobarf00  repeat 10    x000D        console log  Score      ff 1    x000D   x000D         x000D      return funcs sort compare   x000D      x000D   x000D    return benchmark  x000D       x000D  log  Starting benchmark    n    x000D  res   benchmark    x000D  console log  Winner      res 0  0  name            x000D  count   1  x000D  res forEach  r    gt    x000D    log  count             r 0  name     score      Math floor 10000   r 1    res 0  1     100     count    2        winner        speed of winner             Math round r 1    100    100         x000D      x000D  log   nWinner code  n    x000D  log res 0  0  toString     x000D   lt textarea rows  50  cols  80  style  font-size  16  resize none  border  none   id  log  gt  lt  textarea gt  x000D   x000D   x000D       The test will run for 10s   2s  as you click the button    My results  on the same pc    Chrome Linux Ubuntu 64  1  replace1 score  100   winner   766 18  2  replace4 score  99 07  speed of winner   759 11  3  replace3 score  68 36  speed of winner   523 83  4  replace2 score  59 35  speed of winner   454 78   Firefox Linux Ubuntu 64 1  replace3 score  100   winner   3480 1  2  replace1 score  13 06  speed of winner   454 83  3  replace4 score  9 4  speed of winner   327 42  4  replace2 score  4 81  speed of winner   167 46    Nice mess uh   Took the liberty of adding more test results  Chrome Windows 10 1  replace1 score  100   winner   742 49  2  replace4 score  85 58  speed of winner   635 44  3  replace2 score  54 42  speed of winner   404 08  4  replace3 score  50 06  speed of winner   371 73   Firefox Windows 10 1  replace3 score  100   winner   2645 18  2  replace1 score  30 77  speed of winner   814 18  3  replace4 score  22 3  speed of winner   589 97  4  replace2 score  12 51  speed of winner   331 13   Edge Windows 10 1  replace1 score  100   winner   1251 24  2  replace2 score  46 63  speed of winner   583 47  3  replace3 score  44 42  speed of winner   555 92  4  replace4 score  20  speed of winner   250 28    Chrome on Galaxy Note 4  1  replace4 score  100   winner   99 82  2  replace1 score  91 04  speed of winner   90 88  3  replace3 score  70 27  speed of winner   70 15  4  replace2 score  38 25  speed of winner   38 18

User · Answer

What s the fastest I don t know  but I know what s the most readable - that what s shortest and simplest  Even if it s a little bit slower than other solution it s worth to use   So use     string  replace  a    b      string  replace  abc  g   def      And enjoy good code instead of faster  well    1 100000 sec  is not a difference  and ugly one

User · Answer

Use Regex object like this  var regex   new RegExp       g    str   str replace regex          It will replace all occurrence of   into

User · Answer

The easiest would be to use a regular expression with g flag to replace all instances   str replace  foo g   bar     This will replace all occurrences of foo with bar in the string str  If you just have a string  you can convert it to a RegExp object like this   var pattern    foobar       re   new RegExp pattern   g

User · Answer

Also you can try   string split  foo   join  bar

User · Answer

I think the real answer is that it completely depends on what your inputs look like   I created a JsFiddle to try a bunch of these and a couple of my own against various inputs   No matter how I look at the results  I see no clear winner    RegExp wasn t the fastest in any of the test cases  but it wasn t bad either   Split Join approach seems fastest for sparse replacements  This one I wrote seems fastest for small inputs and dense replacements   function replaceAllOneCharAtATime inSource  inToReplace  inReplaceWith        var output         var firstReplaceCompareCharacter   inToReplace charAt 0       var sourceLength   inSource length      var replaceLengthMinusOne   inToReplace length - 1      for var i   0  i  lt  sourceLength  i             var currentCharacter   inSource charAt i           var compareIndex   i          var replaceIndex   0          var sourceCompareCharacter   currentCharacter          var replaceCompareCharacter   firstReplaceCompareCharacter          while true               if sourceCompareCharacter    replaceCompareCharacter               output    currentCharacter              break                    if replaceIndex  gt   replaceLengthMinusOne                i  replaceLengthMinusOne              output    inReplaceWith                was a match             break                    compareIndex    replaceIndex            if i  gt   sourceLength                  not a match             break                    sourceCompareCharacter   inSource charAt compareIndex              replaceCompareCharacter   inToReplace charAt replaceIndex                        replaceCompareCharacter    currentCharacter            return output

User · Answer

Just thinking about it from a speed issue I believe the case sensitive example provided in the link above would be by far the fastest solution   var token     r n   var newToken        var oldStr    This is a test r nof the emergency broadcasting r nsystem    newStr   oldStr split token  join newToken     newStr would be  This is a test of the emergency broadcast system

[javascript] Fastest method to replace all instances of a character in a string

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