How can I match multiple occurrences with a regex in JavaScript similar to PHP s preg match all

Question

I am trying to parse url-encoded strings that are made up of key value pairs separated by either  amp  or  amp amp     The following will only match the first occurrence  breaking apart the keys and values into separate result elements   var result   mystring match      amp   amp amp               amp         The results for the string  1111342 Adam 20Franco amp 348572 Bob 20Jones  would be     1111342    Adam 20Franco     Using the global flag   g   will match all occurrences  but only return the fully matched sub-strings  not the separated keys and values   var result   mystring match      amp   amp amp               amp     g    The results for the string  1111342 Adam 20Franco amp 348572 Bob 20Jones  would be     1111342 Adam 20Franco     amp 348572 Bob 20Jones     While I could split the string on  amp  and break apart each key value pair individually  is there any way using JavaScript s regular expression support to match multiple occurrences of the pattern      amp   amp amp               amp      similar to PHP s preg match all   function   I m aiming for some way to get results with the sub-matches separated like      1111342    348572      Adam 20Franco    Bob 20Jones      or      1111342    Adam 20Franco      348572    Bob 20Jones

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If someone  like me  needs Tomalak s method with array support  ie  multiple select   here it is   function getUrlParams url      var re           amp    amp         amp              amp       g        match  params             decode   function  s   return decodeURIComponent s replace     g              if  typeof url     undefined   url   document location href     while  match   re exec url         if  params decode match 1                if  typeof params decode match 1        object                  params decode match 1      new Array  params decode match 1     decode match 2                else               params decode match 1    push decode match 2                         else         params decode match 1      decode match 2          return params    var urlParams   getUrlParams location search     input  my 1 amp my 2 amp my things  result 1 2 things  earlier returned only  things

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Source  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects RegExp exec  Finding successive matches  If your regular expression uses the  g  flag  you can use the exec   method multiple times to find successive matches in the same string  When you do so  the search starts at the substring of str specified by the regular expression s lastIndex property  test   will also advance the lastIndex property   For example  assume you have this script   var myRe    ab  g  var str    abbcdefabh   var myArray  while   myArray   myRe exec str       null      var msg    Found     myArray 0            msg     Next match starts at     myRe lastIndex    console log msg       This script displays the following text   Found abb  Next match starts at 3 Found ab  Next match starts at 912   Note  Do not place the regular expression literal  or RegExp constructor  within the while condition or it will create an infinite loop if there is a match due to the lastIndex property being reset upon each iteration  Also be sure that the global flag is set or a loop will occur here also

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You need to use the  g  switch for a global search  var result   mystring match    amp   amp amp               amp     g

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2020 edit  Use URLSearchParams  as this job no longer requires any kind of custom code  Browsers can do this for you with a single constructor   const str    1111342 Adam 20Franco amp 348572 Bob 20Jones   const data   new URLSearchParams str   for  pair of data  console log pair    yields  Array    1111342    Adam Franco    Array    348572    Bob Jones      So there is no reason to use regex for this anymore   Original answer  If you don t want to rely on the  blind matching  that comes with running exec style matching  JavaScript does come with match-all functionality built in  but it s part of the replace function call  when using a  what to do with the capture groups  handling function   var data        var getKeyValue   function fullPattern  group1  group2  group3      data group2    group3      mystring replace      amp   amp amp               amp     g  getKeyValue     done   Instead of using the capture group handling function to actually return replacement strings  for replace handling  the first arg is the full pattern match  and subsequent args are individual capture groups  we simply take the groups 2 and 3 captures  and cache that pair   So  rather than writing complicated parsing functions  remember that the  matchAll  function in JavaScript is simply  replace  with a replacement handler function  and much pattern matching efficiency can be had

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Hoisted from the comments     2020 comment  rather than using regex  we now have URLSearchParams  which does all of this for us  so no custom code  let alone regex  are necessary anymore             Mike  Pomax  Kamermans   Browser support is listed here https   caniuse com  feat urlsearchparams    I would suggest an alternative regex  using sub-groups to capture name and value of the parameters individually and re exec     function getUrlParams url      var re           amp    amp         amp              amp       g        match  params             decode   function  s   return decodeURIComponent s replace     g              if  typeof url     undefined   url   document location href     while  match   re exec url         params decode match 1      decode match 2          return params     var result   getUrlParams  http   maps google de maps f q amp source s q amp hl de amp geocode  amp q Frankfurt am Main amp sll 50 106047 8 679886 amp sspn 0 370369 0 833588 amp ie UTF8 amp ll 50 116616 8 680573 amp spn 0 35972 0 833588 amp z 11 amp iwloc addr      result is an object        f   q    geocode       hl   de    ie   UTF8    iwloc   addr    ll   50 116616 8 680573    q   Frankfurt am Main    sll   50 106047 8 679886    source   s q    spn   0 35972 0 833588    sspn   0 370369 0 833588    z   11      The regex breaks down as follows                     non-capturing group                        or          amp            allow   amp amp    for wrongly HTML-encoded URLs                   end non-capturing group                  group 1                    any character except          or      at least once                  end group 1 - this will be the parameter s name                  non-capturing group                    an      optional                    group 2                      any character except     or      any number of times                    end group 2 - this will be the parameter s value                  end non-capturing group

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Set the g modifier for a global match        g

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Use window URL    gt  s    http   www example com index html 1111342 Adam 20Franco amp 348572 Bob 20Jones   gt  u   new URL s   gt  Array from u searchParams entries       1111342    Adam Franco      348572    Bob Jones

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To capture several parameters using the same name  I modified the while loop in Tomalak s method like this     while  match   re exec url         var pName   decode match 1        var pValue   decode match 2        params pName    params pName  push pValue    params pName     pValue         input   firstname george amp lastname bush amp firstname bill amp lastname clinton   returns   firstname     george    bill    lastname     bush    clinton

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H llo from 2020  Let me bring String prototype matchAll   to your attention   let regexp        amp   amp amp               amp     g  let str    1111342 Adam 20Franco amp 348572 Bob 20Jones    for  let match of str matchAll regexp         let  full  key  value    match      console log key       gt      value       Outputs   1111342   gt  Adam 20Franco 348572   gt  Bob 20Jones

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For capturing groups  I m used to using preg match all in PHP and I ve tried to replicate it s functionality here    lt script gt      Return all pattern matches with captured groups RegExp prototype execAll   function string        var match   null      var matches   new Array        while  match   this exec string             var matchArray               for  i in match                if  parseInt i     i                    matchArray push match i                                    matches push matchArray             return matches        Example var someTxt    abc123 def456 ghi890   var results     a-z    d   g execAll someTxt       Output    abc123    123       def456    456       ghi890    890      lt  script gt

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If you can get away with using map this is a four-line-solution    x000D   x000D  var mystring    1111342 Adam 20Franco amp 348572 Bob 20Jones   x000D   x000D  var result   mystring match    amp   amp amp               amp     g         x000D  result   result map function i    x000D    return i match    amp   amp amp               amp        x000D      x000D   x000D  console log result   x000D   x000D   x000D    Ain t pretty  ain t efficient  but at least it is compact

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Just to stick with the proposed question as indicated by the title  you can actually iterate over each match in a string using String prototype replace     For example the following does just that to get an array of all words based on a regular expression   function getWords str      var arr         str replace   w  g  function m        arr push m           return arr     var words   getWords  Where in the world is Carmen Sandiego         gt    Where    in    the    world    is    Carmen    Sandiego     If I wanted to get capture groups or even the index of each match I could do that too   The following shows how each match is returned with the entire match  the 1st capture group and the index   function getWords str      var arr         str replace   w          g  function m  remaining  index        arr push   match  m  remainder  remaining  index  index             return arr     var words   getWords  Where in the world is Carmen Sandiego       After running the above  words will be as follows              match    Where        remainder     in the world is Carmen Sandiego         index   0               match    in        remainder     the world is Carmen Sandiego         index   6               match    the        remainder     world is Carmen Sandiego         index   9               match    world        remainder     is Carmen Sandiego         index   13               match    is        remainder     Carmen Sandiego         index   19               match    Carmen        remainder     Sandiego         index   22               match    Sandiego        remainder             index   29         In order to match multiple occurrences similar to what is available in PHP with preg match all you can use this type of thinking to make your own or use something like YourJS matchAll     YourJS more or less defines this function as follows   function matchAll str  rgx      var arr  extras  matches         str replace rgx global   rgx   new RegExp rgx source   rgx       replace    s S     g    g     function         matches push arr      slice call arguments        extras   arr splice -2       arr index   extras 0       arr input   extras 1           return matches 0    matches   null

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Splitting it looks like the best option in to me    1111342 Adam 20Franco amp 348572 Bob 20Jones  split   amp    map x   gt  x match      amp   amp amp               amp

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Well    I had a similar problem    I want an incremental   step search with RegExp   eg  start search    do some processing    continue search until last match   After lots of internet search    like always  this is turning an habit now  I end up in StackOverflow and found the answer     Whats is not referred and matters to mention is  lastIndex  I now understand why the RegExp object implements the  lastIndex  property

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To avoid regex hell you could find your first match  chop off a chunk then attempt to find the next one on the substring  In C  this looks something like this  sorry I ve not ported it over to JavaScript for you           long count   0          var remainder   data          Match match   null          do                       match    rgx Match remainder               if  match Success                                count                    remainder   remainder Substring match Index   1  remainder Length -  match Index 1                            while  match Success           return count

[javascript] How can I match multiple occurrences with a regex in JavaScript similar to PHP's preg_match_all()?

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