Insert a string at a specific index

Question

How can I insert a string at a specific index of another string     var txt1    foo baz    Suppose I want to insert  bar   after the  foo  how can I achieve that   I thought of substring    but there must be a simpler more straight forward way

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my string             hello world   my insert              dear   my insert location   5   my string   my string split        my string splice  my insert location   0  my insert    my string   my string join        https   jsfiddle net gaby de wilde wz69nw9k

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You could prototype your own splice   into String   Polyfill  if   String prototype splice                    JSDoc                The splice   method changes the content of a string by removing a range of        characters and or adding new characters                 this  String          param  number  start Index at which to start changing the string          param  number  delCount An integer indicating the number of old chars to remove          param  string  newSubStr The String that is spliced in          return  string  A new string with the spliced substring              String prototype splice   function start  delCount  newSubStr            return this slice 0  start    newSubStr   this slice start   Math abs delCount               Example   x000D   x000D  String prototype splice   function idx  rem  str    x000D      return this slice 0  idx    str   this slice idx   Math abs rem    x000D     x000D   x000D  var result    foo baz  splice 4  0   bar     x000D   x000D  document body innerHTML   result      foo bar baz  x000D   x000D   x000D      EDIT  Modified it to ensure that rem is an absolute value

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UPDATE 2016  Here is another just-for-fun  but more serious   prototype function based on one-liner RegExp approach  with prepend support on undefined or negative index           Insert  what  to string at position  index       String prototype insert   function what  index        return index  gt  0           this replace new RegExp        index            amp     what            what   this      console log   foo baz  insert  bar    4          foo bar baz  console log   foo baz  insert  bar               bar foo baz      Previous  back to 2012  just-for-fun solution   var index   4      what     bar      foo baz  replace    g  function v  i        return i     index - 1   v   what   v           foo bar baz

User · Answer

Given your current example you could achieve the result by either  var txt2   txt1 split      join   bar      or  var txt2   txt1 replace        bar       but given that you can make such assumptions  you might as well skip directly to Gullen s example   In a situation where you really can t make any assumptions other than character index-based  then I really would go for a substring solution

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Well  we can use both the substring and slice method  String prototype customSplice   function  index  absIndex  string        return this slice 0  index    string  this slice index   Math abs absIndex         String prototype replaceString   function  index  string        if  index  gt  0          return this substring 0  index    string   this substr index        return string   this       console log  Hello Developers  customSplice 6 0  Stack        Hello Stack Developers console log  Hello Developers  replaceString 6  Stack          Hello Stack Developers  The only problem of a substring method is that it won t work with a negative index  It s always take string index from 0th position

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Take the solution  I have written this code in an easy format  const insertWord    sentence word index    gt        var sliceWord   word slice  quot  quot   output      join     Slicing the input word and declaring other variables     var sliceSentence   sentence slice  quot  quot       Slicing the input sentence into each alphabets     for  var i   0  i  lt  sliceSentence length  i                          if  i     index                       checking if index of array     input index             for  var j   0  j  lt  word length  j                                   if yes we ll insert the word                 output push sliceWord j       Condition is true we are inserting the word                                      output push  quot   quot       providing a single space at the end of the word                            output push sliceSentence i        pushing the remaining elements present in an array                   join   output join  quot  quot       converting an array to string     console log join      return join

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If anyone is looking for a way to insert text at multiple indices in a string  try this out   String prototype insertTextAtIndices   function text        return this replace    g  function character  index            return text index    text index    character   character               For example  you can use this to insert  lt span gt  tags at certain offsets in a string   var text         6    lt span gt        11    lt  span gt        Hello world   insertTextAtIndices text      returns  Hello  lt span gt world lt  span gt

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Here is a method I wrote that behaves like all other programming languages   x000D   x000D  String prototype insert   function index  string      if  index  gt  0        return this substring 0  index    string   this substr index          return string   this        Example of use  var something    How you    something   something insert 3    are    console log something  x000D   x000D   x000D   Reference   http   coderamblings wordpress com 2012 07 09 insert-a-string-at-a-specific-index

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Just make the following function   function insert str  index  value        return str substr 0  index    value   str substr index       and then use it like that   alert insert  foo baz   4   bar        Output  foo bar baz  It behaves exactly  like the C   Sharp  String Insert int startIndex  string value    NOTE  This insert function inserts the string value  third parameter  before the specified integer index  second parameter  in the string str  first parameter   and then returns the new string without changing str

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I wanted to compare the method using substring and the method using slice from Base33 and user113716 respectively  to do that I wrote some code also have a look at this performance comparison  substring  slice The code I used creates huge strings and inserts the string  quot bar  quot  multiple times into the huge string  x000D   x000D  if   String prototype splice                    JSDoc                The splice   method changes the content of a string by removing a range of        characters and or adding new characters                 this  String          param  number  start Index at which to start changing the string          param  number  delCount An integer indicating the number of old chars to remove          param  string  newSubStr The String that is spliced in          return  string  A new string with the spliced substring              String prototype splice   function  start  delCount  newSubStr            return this slice 0  start    newSubStr   this slice start   Math abs delCount              String prototype splice   function  idx  rem  str        return this slice 0  idx    str   this slice idx   Math abs rem         String prototype insert   function  index  string        if  index  gt  0          return this substring 0  index    string   this substring index  this length        return string   this       function createString size        var s          for  var i   0  i  lt  size  i              s     Some String             return s     function testSubStringPerformance str  times        for  var i   0  i  lt  times  i            str insert 4   bar       function testSpliceStringPerformance str  times        for  var i   0  i  lt  times  i            str splice 4  0   bar        function doTests repeatMax  sSizeMax        n   1000     sSize   1000     for  var i   1  i  lt   repeatMax  i              var repeatTimes   n    10   i          for  var j   1  j  lt   sSizeMax  j                  var actualStringSize   sSize     10   j              var s1   createString actualStringSize              var s2   createString actualStringSize              var start   performance now               testSubStringPerformance s1  repeatTimes              var end   performance now               var subStrPerf   end - start              start   performance now               testSpliceStringPerformance s2  repeatTimes              end   performance now               var splicePerf   end - start              console log                   string size                Some String   length   actualStringSize    n                    repeat count               repeatTimes    n                    splice performance         splicePerf    n                    substring performance      subStrPerf    n                    difference      splicePerf - subStrPerf         splice is faster  -   subStr is faster                                       doTests 1  100  x000D   x000D   x000D   The general difference in performance is marginal at best and both methods work just fine  even on strings of length    12000000

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I know this is an old thread  however  here is a really effective approach   var tn   document createTextNode  I am just  to help   t insertData 10   trying      What s great about this is that it coerces the node content  So if this node were already on the DOM  you wouldn t need to use any query selectors or update the innerText  The changes would reflect due to its binding   Were you to need a string  simply access the node s text content property   tn textContent    gt   I am just trying to help

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Inserting at a specific index  rather than  say  at the first space character  has to use string slicing substring   var txt2   txt1 slice 0  3     bar    txt1 slice 3

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Using slice  You can use slice 0 index    str   slice index   Or you can create a method for it    x000D   x000D  String prototype insertAt   function index str   x000D    return this slice 0 index    str   this slice index  x000D    x000D  console log  foo bar  insertAt 4  baz       foo baz bar x000D   x000D   x000D    Splice method for Strings  You can split   the main string and add then use normal splice     x000D   x000D  String prototype splice   function index del    newStrs   x000D    let str   this split      x000D    str splice index del newStrs join             x000D    return str join      x000D    x000D   x000D   x000D   var txt1    foo baz  x000D   x000D    inserting single string  x000D  console log txt1 splice 4 0  bar        foo bar baz x000D   x000D   x000D    inserting multiple strings x000D  console log txt1 splice 4 0  bar    bar2        foo bar bar2 baz x000D   x000D   x000D    removing letters x000D  console log txt1 splice 1 2     f baz x000D   x000D   x000D    remving and inseting atm x000D  console log txt1 splice 1 2   bar      f bar baz x000D   x000D   x000D    Applying splice   at multiple indexes  The method takes an array of arrays each element of array representing a single splice      x000D   x000D  String prototype splice   function index del    newStrs   x000D    let str   this split      x000D    str splice index del newStrs join             x000D    return str join      x000D    x000D   x000D   x000D  String prototype mulSplice   function arr   x000D    str   this x000D    let dif   0  x000D     x000D    arr forEach x   gt    x000D      x 2      x 2         x000D      x 1      x 1     0  x000D      str   str splice x 0    dif x 1     x 2    x000D      dif    x 2  join     length - x 1   x000D       x000D    return str  x000D    x000D   x000D  let txt    foo bar baz  x000D   x000D    Replacing the  foo  and  bar  with  something1    another  x000D  console log txt splice 0 3  something    x000D  console log txt mulSplice  x000D    x000D   0 3   something1     x000D   4 3   another    x000D    x000D   x000D     x000D   x000D   x000D

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Instantiate an array from the string Use Array splice Stringify again using Array join   The benefits of this approach are two-fold    Simple Unicode code point compliant    x000D   x000D  const pair   Array from  USDGBP   x000D  pair splice 3  0       x000D  console log pair join      x000D   x000D   x000D

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You can do it easily with regexp in one line of code   x000D   x000D  const str    Hello RegExp    x000D  const index   6  x000D  const insert    Lovely    x000D       x000D     Hello RegExp   replace      6          1Lovely  2    x000D  const res   str replace new RegExp        index            1  insert  2    x000D       x000D  console log res   x000D   x000D   x000D     Hello Lovely RegExp

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This is basically doing what  Base33 is doing except I m also giving the option of using a negative index to count from the end   Kind of like the substr method allows     use a negative index to insert relative to the end of the string   String prototype insert   function  index  string      var ind   index  lt  0   this length   index     index    return  this substring 0  ind    string   this substr ind       Example  Let s say you have full size images using a naming convention but can t update the data to also provide thumbnail urls  var url     images myimage jpg   var thumb   url insert -4    thm           result     images myimage thm jpg

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You can use Regular Expressions with a dynamic pattern   var text    something   var output                           var pattern   new RegExp     s   text length       var output replace pattern text     outputs     something          This replaces text length of whitespace characters at the beginning of the string output  The RegExp means    - beginning of a line  s any white space character  repeated  n  times  in this case text length  Use    to   escape backslashes when building this kind of patterns out of strings

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another solution  cut the string in 2 and put a string in between   var str   jQuery   selector   text     var strlength   str length   strf   str substr 0   strlength - 5   strb   str substr strlength - 5   5    jQuery   selector   html strf    inserted    strb

[javascript] Insert a string at a specific index

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