How do you use a variable in a regular expression

Question

I would like to create a String replaceAll   method in JavaScript and I m thinking that using a regex would be most terse way to do it   However  I can t figure out how to pass a variable in to a regex   I can do this already which will replace all the instances of  B  with  A     ABABAB  replace  B g   A      But I want to do something like this   String prototype replaceAll   function replaceThis  withThis        this replace  replaceThis g  withThis        But obviously this will only replace the text  replaceThis    so how do I pass this variable in to my regex string

User · Answer

To satisfy my need to insert a variable alias function into a Regular Expression  this is what I came up with   oldre    xx         function newre e       return RegExp e toString   replace     g     replace  xx g  yy    g       String prototype replaceAll   this replace newre oldre    withThis      where  oldre  is the original regexp that I want to insert a variable   xx  is the placeholder for that variable alias function  and  yy  is the actual variable name  alias  or function

User · Answer

String prototype replaceAll   function  replaceThis  withThis       var re   new RegExp replaceThis  g        return this replace re  withThis      var aa    abab54  aba  replaceAll         v      Test with this tool

User · Answer

None of these answers were clear to me  I eventually found a good explanation at http   burnignorance com php-programming-tips how-to-use-a-variable-in-replace-function-of-javascript   The simple answer is   var search term   new RegExp search term   g        text   text replace search term  replace term     For example    x000D   x000D     button   click function     x000D    Find and replace  Lorem    Chocolate    x000D    Find and replace  ipsum    ice-cream    x000D      x000D   x000D  function Find and replace search term  replace term    x000D    text      textbox   html    x000D    var search term   new RegExp search term   g    x000D    text   text replace search term  replace term   x000D       textbox   html text   x000D    x000D   lt script src  https   ajax googleapis com ajax libs jquery 2 1 1 jquery min js  gt  lt  script gt  x000D   lt textbox gt  x000D    Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum x000D   lt  textbox gt  x000D   lt button gt Click me lt  button gt  x000D   x000D   x000D

User · Answer

This   var txt new RegExp pattern attributes     is equivalent to this   var txt  pattern attributes    See http   www w3schools com jsref jsref obj regexp asp

User · Answer

this replace  new RegExp  replaceThis   g     withThis

User · Answer

As Eric Wendelin mentioned  you can do something like this   str1    pattern  var re   new RegExp str1   g     pattern matching    replace re   regex      This yields  regex matching     However  it will fail if str1 is      You d expect the result to be  pattern matching regex   replacing the period with  regex   but it ll turn out to be     regexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregex   This is because  although     is a String  in the RegExp constructor it s still interpreted as a regular expression  meaning any non-line-break character  meaning every character in the string  For this purpose  the following function may be useful    RegExp quote   function str         return str replace                    -   g      1          Then you can do   str1       var re   new RegExp RegExp quote str1    g     pattern matching    replace re   regex      yielding  pattern matching regex

User · Answer

While you can make dynamically-created RegExp s  as per the other responses to this question   I ll echo my comment from a similar post  The functional form of String replace   is extremely useful and in many cases reduces the need for dynamically-created RegExp objects   which are kind of a pain  cause you have to express the input to the RegExp constructor as a string rather than use the slashes   A-Z    regexp literal format

User · Answer

As Eric Wendelin mentioned  you can do something like this   str1    pattern  var re   new RegExp str1   g     pattern matching    replace re   regex      This yields  regex matching     However  it will fail if str1 is      You d expect the result to be  pattern matching regex   replacing the period with  regex   but it ll turn out to be     regexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregex   This is because  although     is a String  in the RegExp constructor it s still interpreted as a regular expression  meaning any non-line-break character  meaning every character in the string  For this purpose  the following function may be useful    RegExp quote   function str         return str replace                    -   g      1          Then you can do   str1       var re   new RegExp RegExp quote str1    g     pattern matching    replace re   regex      yielding  pattern matching regex

User · Answer

You can always use indexOf repeatedly   String prototype replaceAll   function substring  replacement        var result           var lastIndex   0       while true            var index   this indexOf substring  lastIndex           if index     -1  break          result    this substring lastIndex  index    replacement          lastIndex   index   substring length             return result   this substring lastIndex        This doesn   t go into an infinite loop when the replacement contains the match

User · Answer

String prototype replaceAll   function a  b        return this replace new RegExp a replace                    -   ig      1     ig    b      Test it like   var whatever    Some  b random  b  text in a  b sentence   b    console log whatever replaceAll        lt    replaceAll        gt

User · Answer

None of these answers were clear to me  I eventually found a good explanation at http   burnignorance com php-programming-tips how-to-use-a-variable-in-replace-function-of-javascript   The simple answer is   var search term   new RegExp search term   g        text   text replace search term  replace term     For example    x000D   x000D     button   click function     x000D    Find and replace  Lorem    Chocolate    x000D    Find and replace  ipsum    ice-cream    x000D      x000D   x000D  function Find and replace search term  replace term    x000D    text      textbox   html    x000D    var search term   new RegExp search term   g    x000D    text   text replace search term  replace term   x000D       textbox   html text   x000D    x000D   lt script src  https   ajax googleapis com ajax libs jquery 2 1 1 jquery min js  gt  lt  script gt  x000D   lt textbox gt  x000D    Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum x000D   lt  textbox gt  x000D   lt button gt Click me lt  button gt  x000D   x000D   x000D

User · Answer

Instead of using the  regex g syntax  you can construct a new RegExp object   var replace    regex   var re   new RegExp replace  g      You can dynamically create regex objects this way  Then you will do    mystring  replace re   newstring

User · Answer

As Eric Wendelin mentioned  you can do something like this   str1    pattern  var re   new RegExp str1   g     pattern matching    replace re   regex      This yields  regex matching     However  it will fail if str1 is      You d expect the result to be  pattern matching regex   replacing the period with  regex   but it ll turn out to be     regexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregex   This is because  although     is a String  in the RegExp constructor it s still interpreted as a regular expression  meaning any non-line-break character  meaning every character in the string  For this purpose  the following function may be useful    RegExp quote   function str         return str replace                    -   g      1          Then you can do   str1       var re   new RegExp RegExp quote str1    g     pattern matching    replace re   regex      yielding  pattern matching regex

User · Answer

You want to build the regular expression dynamically and for this the proper solutuion is to use the new RegExp string  constructor  In order for constructor to treat special characters literally  you must escape them  There is a built-in function in jQuery UI autocomplete widget called   ui autocomplete escapeRegex            you can make use of the built-in     ui autocomplete escapeRegex function  It ll take a single string   argument and escape all regex characters  making the result safe to   pass to new RegExp      If you are using jQuery UI you can use that function  or copy its definition from the source   function escapeRegex  value         return value replace     -                     s  g       amp          And use it like this     z-a  z-a  z-a   replace new RegExp escapeRegex   z-a      g      a-z                   escapeRegex   z-a          - gt     z -a       new RegExp escapeRegex   z-a      g   - gt     z -a   g    end result                            - gt    a-z  a-z  a-z

User · Answer

While you can make dynamically-created RegExp s  as per the other responses to this question   I ll echo my comment from a similar post  The functional form of String replace   is extremely useful and in many cases reduces the need for dynamically-created RegExp objects   which are kind of a pain  cause you have to express the input to the RegExp constructor as a string rather than use the slashes   A-Z    regexp literal format

User · Answer

String prototype replaceAll   function  replaceThis  withThis       var re   new RegExp replaceThis  g        return this replace re  withThis      var aa    abab54  aba  replaceAll         v      Test with this tool

User · Answer

You want to build the regular expression dynamically and for this the proper solutuion is to use the new RegExp string  constructor  In order for constructor to treat special characters literally  you must escape them  There is a built-in function in jQuery UI autocomplete widget called   ui autocomplete escapeRegex            you can make use of the built-in     ui autocomplete escapeRegex function  It ll take a single string   argument and escape all regex characters  making the result safe to   pass to new RegExp      If you are using jQuery UI you can use that function  or copy its definition from the source   function escapeRegex  value         return value replace     -                     s  g       amp          And use it like this     z-a  z-a  z-a   replace new RegExp escapeRegex   z-a      g      a-z                   escapeRegex   z-a          - gt     z -a       new RegExp escapeRegex   z-a      g   - gt     z -a   g    end result                            - gt    a-z  a-z  a-z

User · Answer

this replace  new RegExp  replaceThis   g     withThis

User · Answer

If you want to get ALL occurrences  g   be case insensitive  i   and use boundaries so that it isn t a word within another word    b    re   new RegExp    b  replaceThis   b    gi        Example   let inputString    I m John  or johnny  but I prefer john    let replaceThis    John   let re   new RegExp    b  replaceThis   b    gi    console log inputString replace re   Jack        I m Jack  or johnny  but I prefer Jack

User · Answer

This self calling function will iterate over replacerItems using an index  and change replacerItems index  globally on the string with each pass        const replacerItems     a    b    c             function replacer str  index             const item   replacerItems index             const regex   new RegExp     item      g              const newStr   str replace regex   z              if  index  lt  replacerItems length - 1                return replacer newStr  index   1                         return newStr            console log replacer  abcdefg   0   will output  zzzdefg

User · Answer

Your solution is here   Pass a variable to regular expression   The one which I have implemented is by taking the value from a text field which is the one you want to replace and another is the  replace with  text field  getting the value from text-field in a variable and setting the variable to RegExp function to further replace  In my case I am using Jquery  you also can do it by only JavaScript too   JavaScript code     var replace  document getElementById  replace        getting a value from a text field with I want to replace   var replace with   document getElementById  with      Getting the value from another text fields with which I want to replace another string     var sRegExInput   new RegExp replace   g             body   children   each function           this  html   this  html   replace sRegExInput replace with            This code is on Onclick event of a button  you can put this in a function to call   So now You can pass variable in replace function

User · Answer

String prototype replaceAll   function  replaceThis  withThis       var re   new RegExp replaceThis  g        return this replace re  withThis      var aa    abab54  aba  replaceAll         v      Test with this tool

User · Answer

And the coffeescript version of Steven Penny s answer  since this is  2 google result    even if coffee is just javascript with a lot of characters removed       baz    foo  filter   new RegExp baz    d    food fight  match filter  0     food   and in my particular case  robot name hubot filter   new RegExp robot name  if msg match input match filter    console log  True

User · Answer

To satisfy my need to insert a variable alias function into a Regular Expression  this is what I came up with   oldre    xx         function newre e       return RegExp e toString   replace     g     replace  xx g  yy    g       String prototype replaceAll   this replace newre oldre    withThis      where  oldre  is the original regexp that I want to insert a variable   xx  is the placeholder for that variable alias function  and  yy  is the actual variable name  alias  or function

User · Answer

this replace  new RegExp  replaceThis   g     withThis

User · Answer

For multiple replace without regular expressions I went with the following         let str    I am a cat man  I like cats         let find    cat         let replace    dog              Count how many occurrences there are of the string to find           inside the str to be examined        let findCount   str split find  length - 1         let loopCount   0         while  loopCount  lt  findCount                   str   str replace find  replace           loopCount   loopCount   1                   console log str            I am a dog man  I like dogs   The important part of the solution was found here

User · Answer

Instead of using the  regex g syntax  you can construct a new RegExp object   var replace    regex   var re   new RegExp replace  g      You can dynamically create regex objects this way  Then you will do    mystring  replace re   newstring

User · Answer

This   var txt new RegExp pattern attributes     is equivalent to this   var txt  pattern attributes    See http   www w3schools com jsref jsref obj regexp asp

User · Answer

For multiple replace without regular expressions I went with the following         let str    I am a cat man  I like cats         let find    cat         let replace    dog              Count how many occurrences there are of the string to find           inside the str to be examined        let findCount   str split find  length - 1         let loopCount   0         while  loopCount  lt  findCount                   str   str replace find  replace           loopCount   loopCount   1                   console log str            I am a dog man  I like dogs   The important part of the solution was found here

User · Answer

Instead of using the  regex g syntax  you can construct a new RegExp object   var replace    regex   var re   new RegExp replace  g      You can dynamically create regex objects this way  Then you will do    mystring  replace re   newstring

User · Answer

For anyone looking to use variable with the match method  this worked for me  var alpha    fig    food fight  match alpha    ht   0      fight

User · Answer

ABABAB  replace  B g   A      As always  don t use regex unless you have to  For a simple string replace  the idiom is    ABABAB  split  B   join  A     Then you don t have to worry about the quoting issues mentioned in Gracenotes s answer

User · Answer

Instead of using the  regex g syntax  you can construct a new RegExp object   var replace    regex   var re   new RegExp replace  g      You can dynamically create regex objects this way  Then you will do    mystring  replace re   newstring

User · Answer

String prototype replaceAll   function a  b        return this replace new RegExp a replace                    -   ig      1     ig    b      Test it like   var whatever    Some  b random  b  text in a  b sentence   b    console log whatever replaceAll        lt    replaceAll        gt

User · Answer

You can use this if  1 not work with you  var pattern   new RegExp  amman   i     abc Amman efg  replace pattern   lt b gt    abc Amman efg  match pattern  0    lt  b gt

User · Answer

String prototype replaceAll   function  replaceThis  withThis       var re   new RegExp replaceThis  g        return this replace re  withThis      var aa    abab54  aba  replaceAll         v      Test with this tool

User · Answer

ABABAB  replace  B g   A      As always  don t use regex unless you have to  For a simple string replace  the idiom is    ABABAB  split  B   join  A     Then you don t have to worry about the quoting issues mentioned in Gracenotes s answer

User · Answer

As Eric Wendelin mentioned  you can do something like this   str1    pattern  var re   new RegExp str1   g     pattern matching    replace re   regex      This yields  regex matching     However  it will fail if str1 is      You d expect the result to be  pattern matching regex   replacing the period with  regex   but it ll turn out to be     regexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregexregex   This is because  although     is a String  in the RegExp constructor it s still interpreted as a regular expression  meaning any non-line-break character  meaning every character in the string  For this purpose  the following function may be useful    RegExp quote   function str         return str replace                    -   g      1          Then you can do   str1       var re   new RegExp RegExp quote str1    g     pattern matching    replace re   regex      yielding  pattern matching regex

User · Answer

For anyone looking to use variable with the match method  this worked for me  var alpha    fig    food fight  match alpha    ht   0      fight

User · Answer

This   var txt new RegExp pattern attributes     is equivalent to this   var txt  pattern attributes    See http   www w3schools com jsref jsref obj regexp asp

User · Answer

Here s another replaceAll implementation       String prototype replaceAll   function  stringToFind  stringToReplace            if   stringToFind    stringToReplace  return this          var temp   this          var index   temp indexOf stringToFind           while  index    -1                temp   temp replace stringToFind  stringToReplace               index   temp indexOf stringToFind                     return temp

User · Answer

This self calling function will iterate over replacerItems using an index  and change replacerItems index  globally on the string with each pass        const replacerItems     a    b    c             function replacer str  index             const item   replacerItems index             const regex   new RegExp     item      g              const newStr   str replace regex   z              if  index  lt  replacerItems length - 1                return replacer newStr  index   1                         return newStr            console log replacer  abcdefg   0   will output  zzzdefg

User · Answer

While you can make dynamically-created RegExp s  as per the other responses to this question   I ll echo my comment from a similar post  The functional form of String replace   is extremely useful and in many cases reduces the need for dynamically-created RegExp objects   which are kind of a pain  cause you have to express the input to the RegExp constructor as a string rather than use the slashes   A-Z    regexp literal format

User · Answer

If you want to get ALL occurrences  g   be case insensitive  i   and use boundaries so that it isn t a word within another word    b    re   new RegExp    b  replaceThis   b    gi        Example   let inputString    I m John  or johnny  but I prefer john    let replaceThis    John   let re   new RegExp    b  replaceThis   b    gi    console log inputString replace re   Jack        I m Jack  or johnny  but I prefer Jack

User · Answer

Here s another replaceAll implementation       String prototype replaceAll   function  stringToFind  stringToReplace            if   stringToFind    stringToReplace  return this          var temp   this          var index   temp indexOf stringToFind           while  index    -1                temp   temp replace stringToFind  stringToReplace               index   temp indexOf stringToFind                     return temp

User · Answer

And the coffeescript version of Steven Penny s answer  since this is  2 google result    even if coffee is just javascript with a lot of characters removed       baz    foo  filter   new RegExp baz    d    food fight  match filter  0     food   and in my particular case  robot name hubot filter   new RegExp robot name  if msg match input match filter    console log  True

User · Answer

ABABAB  replace  B g   A      As always  don t use regex unless you have to  For a simple string replace  the idiom is    ABABAB  split  B   join  A     Then you don t have to worry about the quoting issues mentioned in Gracenotes s answer

User · Answer

This   var txt new RegExp pattern attributes     is equivalent to this   var txt  pattern attributes    See http   www w3schools com jsref jsref obj regexp asp

User · Answer

this replace  new RegExp  replaceThis   g     withThis

User · Answer

You can always use indexOf repeatedly   String prototype replaceAll   function substring  replacement        var result           var lastIndex   0       while true            var index   this indexOf substring  lastIndex           if index     -1  break          result    this substring lastIndex  index    replacement          lastIndex   index   substring length             return result   this substring lastIndex        This doesn   t go into an infinite loop when the replacement contains the match

User · Answer

While you can make dynamically-created RegExp s  as per the other responses to this question   I ll echo my comment from a similar post  The functional form of String replace   is extremely useful and in many cases reduces the need for dynamically-created RegExp objects   which are kind of a pain  cause you have to express the input to the RegExp constructor as a string rather than use the slashes   A-Z    regexp literal format

User · Answer

You can use this if  1 not work with you  var pattern   new RegExp  amman   i     abc Amman efg  replace pattern   lt b gt    abc Amman efg  match pattern  0    lt  b gt

User · Answer

ABABAB  replace  B g   A      As always  don t use regex unless you have to  For a simple string replace  the idiom is    ABABAB  split  B   join  A     Then you don t have to worry about the quoting issues mentioned in Gracenotes s answer

User · Answer

Your solution is here   Pass a variable to regular expression   The one which I have implemented is by taking the value from a text field which is the one you want to replace and another is the  replace with  text field  getting the value from text-field in a variable and setting the variable to RegExp function to further replace  In my case I am using Jquery  you also can do it by only JavaScript too   JavaScript code     var replace  document getElementById  replace        getting a value from a text field with I want to replace   var replace with   document getElementById  with      Getting the value from another text fields with which I want to replace another string     var sRegExInput   new RegExp replace   g             body   children   each function           this  html   this  html   replace sRegExInput replace with            This code is on Onclick event of a button  you can put this in a function to call   So now You can pass variable in replace function

[javascript] How do you use a variable in a regular expression?

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