Regex to extract substring returning 2 results for some reason

Question

I need to do a lot of regex things in javascript but am having some issues with the syntax and I can t seem to find a definitive resource on this   for some reason when I do   var tesst    afskfsd33j  var test   tesst match  a    j    alert  test    it shows    afskfsd33j  fskfsd33    I m not sure why its giving this output of original and the matched string  I am wondering how I can get it to just give the match  essentially extracting the part I want from the original string   Thanks for any advice

User · Answer

Just get rid of the parenthesis and that will give you an array with one element and:

Change this line

var test = tesst.match(/a(.*)j/);

To this

var test = tesst.match(/a.*j/);

If you add parenthesis the match() function will find two match for you one for whole expression and one for the expression inside the parenthesis

Also according to developer.mozilla.org docs :

If you only want the first match found, you might want to use RegExp.exec() instead.

You can use the below code:

RegExp(/a.*j/).exec("afskfsd33j")

User · Answer

Each group defined by parenthesis    is captured during processing and each captured group content is pushed into result array in same order as groups within pattern starts  See more on http   www regular-expressions info brackets html and http   www regular-expressions info refcapture html  choose right language to see supported features   var source    afskfsd33j  var result   source match  a    j     result    afskfsd33j    fskfsd33     The reason why you received this exact result is following   First value in array is the first found string which confirms the entire pattern  So it should definitely start with  a  followed by any number of any characters and ends with first  j  char after starting  a    Second value in array is captured group defined by parenthesis  In your case group contain entire pattern match without content defined outside parenthesis  so exactly  fskfsd33    If you want to get rid of second value in array you may define pattern like this     a      j    where      means that group of chars which match the content in parenthesis will not be part of resulting array   Other options might be in this simple case to write pattern without any group because it is not necessary to use group at all     a  j    If you want to just check whether source text matches the pattern and does not care about which text it found than you may try   var result    a  j  test source     The result should return then only true false values  For more info see http   www javascriptkit com javatutors re3 shtml

User · Answer

I think your problem is that the match method is returning an array  The 0th item in the array is the original string  the 1st thru nth items correspond to the 1st through nth matched parenthesised items  Your  alert    call is showing the entire array

User · Answer

I ve just had the same problem   You only get the text twice in your result if you include a match group  in brackets  and the  g   global  modifier  The first item always is the first result  normally OK when using match reg  on a short string  however when using a construct like   while   result   reg exec string       null       console log result       the results are a little different   Try the following code   var regEx   new RegExp    0-9    cat fish     g    sampleString  1 cat and 2 fish   var result   sample string match regEx   console log JSON stringify result         1 cat   2 fish    var reg   new RegExp   0-9    cat fish    g    sampleString  1 cat and 2 fish   while   result   reg exec sampleString       null        console dir JSON stringify result            1 cat   cat          2 fish   fish     var reg   new RegExp    0-9    cat fish     g    sampleString  1 cat and 2 fish   while   result   reg exec sampleString       null       console dir JSON stringify result            1 cat   1 cat   cat          2 fish   2 fish   fish       tested on recent V8 - Chrome  Node js   The best answer is currently a comment which I can t upvote  so credit to  Mic

User · Answer

match returns an array   The default string representation of an array in JavaScript is the elements of the array separated by commas  In this case the desired result is in the second element of the array   var tesst    afskfsd33j  var test   tesst match  a    j    alert  test 1

[javascript] Regex to extract substring, returning 2 results for some reason

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