Inserting string at position x of another string

Question

I have two variables and need to insert string b into string a at the point represented by position  The result I m looking for is  I want an apple   How can I do this with JavaScript   var a    I want apple   var b     an   var position   6

User · Answer

You can add this function to string class

String.prototype.insert_at=function(index, string)
{   
  return this.substr(0, index) + string + this.substr(index);
}

so that you can use it on any string object:

var my_string = "abcd";
my_string.insertAt(1, "XX");

User · Answer

Using ES6 string literals  would be much shorter    x000D   x000D  const insertAt    str  sub  pos    gt     str slice 0  pos    sub   str slice pos     x000D       x000D  console log insertAt  I want apple     an   6      logs  I want an apple  x000D   x000D   x000D

User · Answer

try  a slice 0 position    b   a slice position     x000D   x000D  var a    I want apple   x000D  var b     an   x000D  var position   6  x000D   x000D  var r  a slice 0 position    b   a slice position   x000D   x000D  console log r   x000D   x000D   x000D    or regexp solution   I want apple  replace      6      1 an      x000D   x000D  var a    I want apple   x000D  var b     an   x000D  var position   6  x000D   x000D  var r  a replace new RegExp        position        1  b   x000D   x000D  console log r   x000D  console log  I want apple  replace      6      1 an     x000D   x000D   x000D

User · Answer

Well just a small change  cause the above solution outputs       I want anapple    instead of       I want an apple    To get the output as       I want an apple    use the following modified code   var output   a substr 0  position          b   a substr position

User · Answer

var array   a split        array splice position  0  b   var output   array join         This would be slower  but will take care of the addition of space before and after the an Also  you ll have to change the value of position   to 2  it s more intuitive now

User · Answer

If ES2018 s lookbehind is available  one more regexp solution  that makes use of it to  replace  at a zero-width position after the Nth character  similar to  Kamil Kielczewski s  but without storing the initial characters in a capturing group     I want apple  replace     lt     6       an      x000D   x000D  var a    I want apple   x000D  var b     an   x000D  var position   6  x000D   x000D  var r  a replace new RegExp     lt       position       b   x000D   x000D  console log r   x000D  console log  I want apple  replace     lt     6       an     x000D   x000D   x000D

User · Answer

var output   a substring 0  position    b   a substring position     Edit  replaced  substr with  substring because  substr is now a legacy function  per https   developer mozilla org en-US docs Web JavaScript Reference Global Objects String substr

User · Answer

Maybe it s even better if you determine position using indexOf   like this   function insertString a  b  at        var position   a indexOf at         if  position     -1                return a substr 0  position    b   a substr position                    return  substring not found       then call the function like this   insertString  I want apple    an     apple      Note  that I put a space after the  an   in the function call  rather than in the return statement

User · Answer

x000D   x000D  var a    I want apple   x000D  var b     an   x000D  var position   6  x000D  var output    a slice 0  position   b  a slice position   join      x000D  console log output   x000D   x000D   x000D      Optional  As a prototype method of String  The following can be used to splice text within another string at a desired index  with an optional removeCount parameter    x000D   x000D  if  String prototype splice     undefined    x000D        x000D       Splices text within a string  x000D        param  int  offset The position to insert the text at  before  x000D        param  string  text The text to insert x000D        param  int   removeCount 0  An optional number of characters to overwrite x000D        returns  string  A modified string containing the spliced text  x000D        x000D    String prototype splice   function offset  text  removeCount 0    x000D      let calculatedOffset   offset  lt  0   this length   offset   offset  x000D      return this substring 0  calculatedOffset    x000D        text   this substring calculatedOffset   removeCount   x000D       x000D    x000D   x000D  let originalText    I want apple   x000D   x000D     Positive offset x000D  console log originalText splice 6    an     x000D     Negative index x000D  console log originalText splice -5   an      x000D     Chaining x000D  console log originalText splice 6    an   splice 2   need   4  splice 0   You   1    x000D   as-console-wrapper   top  0  max-height  100   important    x000D   x000D   x000D

User · Answer

Quick fix  If you don t want to manually add a space  you can do this    x000D   x000D  var a    I want apple   x000D  var b    an   x000D  var position   6  x000D  var output    a slice 0  position   1   b  a slice position   join      x000D  console log output   x000D   x000D   x000D     edit  i see that this is actually answered above  sorry

User · Answer

The Underscore String library has a function that does Insert     insert string  index  substring     string   like so  insert  Hello    6   world         gt   Hello world

[javascript] Inserting string at position x of another string

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